gmock-cookbook.pdf

8/23/13 CookBook - googlemock - Google C++ Mocking Framework Cookbook - Google C++ Mocking Framework - Google Project Hosting
https://code.google.com/p/googlemock/wiki/CookBook 1/41
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Updated Jul 29, 2013 by w...@google.com
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CookBook
Google C++ Mocking Framework Cookbook
Creating Mock Classes
Mocking Private or Protected Methods
Mocking Overloaded Methods
Mocking Class Templates
Mocking Nonvirtual Methods
Mocking Free Functions
The Nice, the Strict, and the Naggy
Simplifying the Interface without Breaking Existing Code
Alternative to Mocking Concrete Classes
Delegating Calls to a Fake
Delegating Calls to a Real Object
Delegating Calls to a Parent Class
Using Matchers
Matching Argument Values Exactly
Using Simple Matchers
Combining Matchers
Casting Matchers
Selecting Between Overloaded Functions
Performing Different Actions Based on the Arguments
Matching Multiple Arguments as a Whole
Using Matchers as Predicates
Using Matchers in Google Test Assertions
Using Predicates as Matchers
Matching Arguments that Are Not Copyable
Validating a Member of an Object
Validating the Value Pointed to by a Pointer Argument
Testing a Certain Property of an Object
Matching Containers
Sharing Matchers
Setting Expectations
Knowing When to Expect
Ignoring Uninteresting Calls
Disallowing Unexpected Calls
Expecting Ordered Calls
Expecting Partially Ordered Calls
Controlling When an Expectation Retires
Using Actions
Returning References from Mock Methods
Returning Live Values from Mock Methods
Combining Actions
Mocking Side Effects
Changing a Mock Object's Behavior Based on the State
Setting the Default Value for a Return Type
Setting the Default Actions for a Mock Method
Using Functions/Methods/Functors as Actions
Invoking a Function/Method/Functor Without Arguments
Invoking an Argument of the Mock Function
Ignoring an Action's Result
Selecting an Action's Arguments

Ignoring Arguments in Action Functions
Sharing Actions
Misc Recipes on Using Google Mock
Making the Compilation Faster
Forcing a Verification
Using Check Points
Mocking Destructors
Using Google Mock and Threads
Controlling How Much Information Google Mock Prints
Gaining Super Vision into Mock Calls
Running Tests in Emacs
Fusing Google Mock Source Files
Extending Google Mock
Writing New Matchers Quickly
Writing New Parameterized Matchers Quickly
Writing New Monomorphic Matchers
Writing New Polymorphic Matchers
Writing New Cardinalities
Writing New Actions Quickly
Writing New Parameterized Actions Quickly
Restricting the Type of an Argument or Parameter in an ACTION
Writing New Action Templates Quickly
Using the ACTION Object's Type
Writing New Monomorphic Actions
Writing New Polymorphic Actions
Teaching Google Mock How to Print Your Values
You can find recipes for using Google Mock here. If you haven't yet, please read the ForDummies document first to make sure you understand
the basics.
Note: Google Mock lives in the t
e
s
t
i
n
gname space. For readability, it is recommended to write u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
F
o
o
;once in your file
before using the name F
o
odefined by Google Mock. We omit such u
s
i
n
gstatements in this page for brevity, but you should do it in your own
code.
Creating Mock Classes
Mocking Private or Protected Methods
You must always put a mock method definition (M
O
C
K
_
M
E
T
H
O
D
*
) in a p
u
b
l
i
c
:section of the mock class, regardless of the method being mocked
being p
u
b
l
i
c
, p
r
o
t
e
c
t
e
d
, or p
r
i
v
a
t
ein the base class. This allows O
N
_
C
A
L
Land E
X
P
E
C
T
_
C
A
L
Lto reference the mock function from outside of
the mock class. (Yes, C++ allows a subclass to change the access level of a virtual function in the base class.) Example:
c
l
a
s
s F
o
o {
p
u
b
l
i
c
:
.
.
.
v
i
r
t
u
a
l b
o
o
l T
r
a
n
s
f
o
r
m
(
G
a
d
g
e
t
* g
) = 0
;
p
r
o
t
e
c
t
e
d
:
v
i
r
t
u
a
l v
o
i
d R
e
s
u
m
e
(
)
;
p
r
i
v
a
t
e
:
v
i
r
t
u
a
l i
n
t G
e
t
T
i
m
e
O
u
t
(
)
;
}
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
T
r
a
n
s
f
o
r
m
, b
o
o
l
(
G
a
d
g
e
t
* g
)
)
;
/
/ T
h
e f
o
l
l
o
w
i
n
g m
u
s
t b
e i
n t
h
e p
u
b
l
i
c s
e
c
t
i
o
n
, e
v
e
n t
h
o
u
g
h t
h
e
/
/ m
e
t
h
o
d
s a
r
e p
r
o
t
e
c
t
e
d o
r p
r
i
v
a
t
e i
n t
h
e b
a
s
e c
l
a
s
s
.
M
O
C
K
_
M
E
T
H
O
D
0
(
R
e
s
u
m
e
, v
o
i
d
(
)
)
;
M
O
C
K
_
M
E
T
H
O
D
0
(
G
e
t
T
i
m
e
O
u
t
, i
n
t
(
)
)
;
}
;
Mocking Overloaded Methods

You can mock overloaded functions as usual. No special attention is required:
c
l
a
s
s F
o
o {
.
.
.
/
/ M
u
s
t b
e v
i
r
t
u
a
l a
s w
e
'
l
l i
n
h
e
r
i
t f
r
o
m F
o
o
.
v
i
r
t
u
a
l ~
F
o
o
(
)
;
/
/ O
v
e
r
l
o
a
d
e
d o
n t
h
e t
y
p
e
s a
n
d
/
o
r n
u
m
b
e
r
s o
f a
r
g
u
m
e
n
t
s
.
v
i
r
t
u
a
l i
n
t A
d
d
(
E
l
e
m
e
n
t x
)
;
v
i
r
t
u
a
l i
n
t A
d
d
(
i
n
t t
i
m
e
s
, E
l
e
m
e
n
t x
)
;
/
/ O
v
e
r
l
o
a
d
e
d o
n t
h
e c
o
n
s
t
-
n
e
s
s o
f t
h
i
s o
b
j
e
c
t
.
v
i
r
t
u
a
l B
a
r
& G
e
t
B
a
r
(
)
;
v
i
r
t
u
a
l c
o
n
s
t B
a
r
& G
e
t
B
a
r
(
) c
o
n
s
t
;
}
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
A
d
d
, i
n
t
(
E
l
e
m
e
n
t x
)
)
;
M
O
C
K
_
M
E
T
H
O
D
2
(
A
d
d
, i
n
t
(
i
n
t t
i
m
e
s
, E
l
e
m
e
n
t x
)
;
M
O
C
K
_
M
E
T
H
O
D
0
(
G
e
t
B
a
r
, B
a
r
&
(
)
)
;
M
O
C
K
_
C
O
N
S
T
_
M
E
T
H
O
D
0
(
G
e
t
B
a
r
, c
o
n
s
t B
a
r
&
(
)
)
;
}
;
Note: if you don't mock all versions of the overloaded method, the compiler will give you a warning about some methods in the base class being
hidden. To fix that, use u
s
i
n
gto bring them in scope:
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
.
.
.
u
s
i
n
g F
o
o
:
:
A
d
d
;
M
O
C
K
_
M
E
T
H
O
D
1
(
A
d
d
, i
n
t
(
E
l
e
m
e
n
t x
)
)
;
/
/ W
e d
o
n
'
t w
a
n
t t
o m
o
c
k i
n
t A
d
d
(
i
n
t t
i
m
e
s
, E
l
e
m
e
n
t x
)
;
.
.
.
}
;
Mocking Class Templates
To mock a class template, append _
Tto the M
O
C
K
_
*macros:
t
e
m
p
l
a
t
e <
t
y
p
e
n
a
m
e E
l
e
m
>
c
l
a
s
s S
t
a
c
k
I
n
t
e
r
f
a
c
e {
.
.
.
/
/ M
u
s
t b
e v
i
r
t
u
a
l a
s w
e
'
l
l i
n
h
e
r
i
t f
r
o
m S
t
a
c
k
I
n
t
e
r
f
a
c
e
.
v
i
r
t
u
a
l ~
S
t
a
c
k
I
n
t
e
r
f
a
c
e
(
)
;
v
i
r
t
u
a
l i
n
t G
e
t
S
i
z
e
(
) c
o
n
s
t = 0
;
v
i
r
t
u
a
l v
o
i
d P
u
s
h
(
c
o
n
s
t E
l
e
m
& x
) = 0
;
}
;
t
e
m
p
l
a
t
e <
t
y
p
e
n
a
m
e E
l
e
m
>
c
l
a
s
s M
o
c
k
S
t
a
c
k : p
u
b
l
i
c S
t
a
c
k
I
n
t
e
r
f
a
c
e
<
E
l
e
m
> {
.
.
.
M
O
C
K
_
C
O
N
S
T
_
M
E
T
H
O
D
0
_
T
(
G
e
t
S
i
z
e
, i
n
t
(
)
)
;
M
O
C
K
_
M
E
T
H
O
D
1
_
T
(
P
u
s
h
, v
o
i
d
(
c
o
n
s
t E
l
e
m
& x
)
)
;
}
;
Mocking Nonvirtual Methods
Google Mock can mock nonvirtual functions to be used in what we call hiperf dependency injection.
In this case, instead of sharing a common base class with the real class, your mock class will be unrelated to the real class, but contain
methods with the same signatures. The syntax for mocking nonvirtual methods is the same as mocking virtual methods:
/
/ A s
i
m
p
l
e p
a
c
k
e
t s
t
r
e
a
m c
l
a
s
s
. N
o
n
e o
f i
t
s m
e
m
b
e
r
s i
s v
i
r
t
u
a
l
.
c
l
a
s
s C
o
n
c
r
e
t
e
P
a
c
k
e
t
S
t
r
e
a
m {
p
u
b
l
i
c
:
v
o
i
d A
p
p
e
n
d
P
a
c
k
e
t
(
P
a
c
k
e
t
* n
e
w
_
p
a
c
k
e
t
)
;
c
o
n
s
t P
a
c
k
e
t
* G
e
t
P
a
c
k
e
t
(
s
i
z
e
_
t p
a
c
k
e
t
_
n
u
m
b
e
r
) c
o
n
s
t
;
s
i
z
e
_
t N
u
m
b
e
r
O
f
P
a
c
k
e
t
s
(
) c
o
n
s
t
;
.
.
.

.
.
.
}
;
/
/ A m
o
c
k p
a
c
k
e
t s
t
r
e
a
m c
l
a
s
s
. I
t i
n
h
e
r
i
t
s f
r
o
m n
o o
t
h
e
r
, b
u
t d
e
f
i
n
e
s
/
/ G
e
t
P
a
c
k
e
t
(
) a
n
d N
u
m
b
e
r
O
f
P
a
c
k
e
t
s
(
)
.
c
l
a
s
s M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m {
p
u
b
l
i
c
:
M
O
C
K
_
C
O
N
S
T
_
M
E
T
H
O
D
1
(
G
e
t
P
a
c
k
e
t
, c
o
n
s
t P
a
c
k
e
t
*
(
s
i
z
e
_
t p
a
c
k
e
t
_
n
u
m
b
e
r
)
)
;
M
O
C
K
_
C
O
N
S
T
_
M
E
T
H
O
D
0
(
N
u
m
b
e
r
O
f
P
a
c
k
e
t
s
, s
i
z
e
_
t
(
)
)
;
.
.
.
}
;
Note that the mock class doesn't define A
p
p
e
n
d
P
a
c
k
e
t
(
)
, unlike the real class. That's fine as long as the test doesn't need to call it.
Next, you need a way to say that you want to use C
o
n
c
r
e
t
e
P
a
c
k
e
t
S
t
r
e
a
min production code, and use M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
min tests. Since the
functions are not virtual and the two classes are unrelated, you must specify your choice at compile time (as opposed to run time).
One way to do it is to templatize your code that needs to use a packet stream. More specifically, you will give your code a template type
argument for the type of the packet stream. In production, you will instantiate your template with C
o
n
c
r
e
t
e
P
a
c
k
e
t
S
t
r
e
a
mas the type argument.
In tests, you will instantiate the same template with M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m
. For example, you may write:
t
e
m
p
l
a
t
e <
c
l
a
s
s P
a
c
k
e
t
S
t
r
e
a
m
>
v
o
i
d C
r
e
a
t
e
C
o
n
n
e
c
t
i
o
n
(
P
a
c
k
e
t
S
t
r
e
a
m
* s
t
r
e
a
m
) { .
.
. }
t
e
m
p
l
a
t
e <
c
l
a
s
s P
a
c
k
e
t
S
t
r
e
a
m
>
c
l
a
s
s P
a
c
k
e
t
R
e
a
d
e
r {
p
u
b
l
i
c
:
v
o
i
d R
e
a
d
P
a
c
k
e
t
s
(
P
a
c
k
e
t
S
t
r
e
a
m
* s
t
r
e
a
m
, s
i
z
e
_
t p
a
c
k
e
t
_
n
u
m
)
;
}
;
Then you can use C
r
e
a
t
e
C
o
n
n
e
c
t
i
o
n
<
C
o
n
c
r
e
t
e
P
a
c
k
e
t
S
t
r
e
a
m
>
(
)and P
a
c
k
e
t
R
e
a
d
e
r
<
C
o
n
c
r
e
t
e
P
a
c
k
e
t
S
t
r
e
a
m
>in production code, and use
C
r
e
a
t
e
C
o
n
n
e
c
t
i
o
n
<
M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m
>
(
)and P
a
c
k
e
t
R
e
a
d
e
r
<
M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m
>in tests.
M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m m
o
c
k
_
s
t
r
e
a
m
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
s
t
r
e
a
m
, .
.
.
)
.
.
.
;
.
. s
e
t m
o
r
e e
x
p
e
c
t
a
t
i
o
n
s o
n m
o
c
k
_
s
t
r
e
a
m .
.
.
P
a
c
k
e
t
R
e
a
d
e
r
<
M
o
c
k
P
a
c
k
e
t
S
t
r
e
a
m
> r
e
a
d
e
r
(
&
m
o
c
k
_
s
t
r
e
a
m
)
;
.
.
. e
x
e
r
c
i
s
e r
e
a
d
e
r .
.
.
Mocking Free Functions
It's possible to use Google Mock to mock a free function (i.e. a Cstyle function or a static method). You just need to rewrite your code to use an
interface (abstract class).
Instead of calling a free function (say, O
p
e
n
F
i
l
e
) directly, introduce an interface for it and have a concrete subclass that calls the free function:
c
l
a
s
s F
i
l
e
I
n
t
e
r
f
a
c
e {
p
u
b
l
i
c
:
.
.
.
v
i
r
t
u
a
l b
o
o
l O
p
e
n
(
c
o
n
s
t c
h
a
r
* p
a
t
h
, c
o
n
s
t c
h
a
r
* m
o
d
e
) = 0
;
}
;
c
l
a
s
s F
i
l
e : p
u
b
l
i
c F
i
l
e
I
n
t
e
r
f
a
c
e {
p
u
b
l
i
c
:
.
.
.
v
i
r
t
u
a
l b
o
o
l O
p
e
n
(
c
o
n
s
t c
h
a
r
* p
a
t
h
, c
o
n
s
t c
h
a
r
* m
o
d
e
) {
r
e
t
u
r
n O
p
e
n
F
i
l
e
(
p
a
t
h
, m
o
d
e
)
;
}
}
;
Your code should talk to F
i
l
e
I
n
t
e
r
f
a
c
eto open a file. Now it's easy to mock out the function.
This may seem much hassle, but in practice you often have multiple related functions that you can put in the same interface, so the perfunction
syntactic overhead will be much lower.
If you are concerned about the performance overhead incurred by virtual functions, and profiling confirms your concern, you can combine this
with the recipe for mocking nonvirtual methods.
The Nice, the Strict, and the Naggy
If a mock method has no E
X
P
E
C
T
_
C
A
L
Lspec but is called, Google Mock will print a warning about the "uninteresting call". The rationale is:

New methods may be added to an interface after a test is written. We shouldn't fail a test just because a method it doesn't know about is
called.
However, this may also mean there's a bug in the test, so Google Mock shouldn't be silent either. If the user believes these calls are
harmless, he can add an E
X
P
E
C
T
_
C
A
L
L
(
)to suppress the warning.
However, sometimes you may want to suppress all "uninteresting call" warnings, while sometimes you may want the opposite, i.e. to treat all of
them as errors. Google Mock lets you make the decision on a permockobject basis.
Suppose your test uses a mock class M
o
c
k
F
o
o
:
T
E
S
T
(
.
.
.
) {
M
o
c
k
F
o
o m
o
c
k
_
f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
f
o
o
, D
o
T
h
i
s
(
)
)
;
.
.
. c
o
d
e t
h
a
t u
s
e
s m
o
c
k
_
f
o
o .
.
.
}
If a method of m
o
c
k
_
f
o
oother than D
o
T
h
i
s
(
)is called, it will be reported by Google Mock as a warning. However, if you rewrite your test to use
N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
>instead, the warning will be gone, resulting in a cleaner test output:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
i
c
e
M
o
c
k
;
T
E
S
T
(
.
.
.
) {
N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
> m
o
c
k
_
f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
f
o
o
, D
o
T
h
i
s
(
)
)
;
.
.
. c
o
d
e t
h
a
t u
s
e
s m
o
c
k
_
f
o
o .
.
.
}
N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
>is a subclass of M
o
c
k
F
o
o
, so it can be used wherever M
o
c
k
F
o
ois accepted.
It also works if M
o
c
k
F
o
o
's constructor takes some arguments, as N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
>"inherits" M
o
c
k
F
o
o
's constructors:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
i
c
e
M
o
c
k
;
T
E
S
T
(
.
.
.
) {
N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
> m
o
c
k
_
f
o
o
(
5
, "
h
i
"
)
; /
/ C
a
l
l
s M
o
c
k
F
o
o
(
5
, "
h
i
"
)
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
f
o
o
, D
o
T
h
i
s
(
)
)
;
.
.
. c
o
d
e t
h
a
t u
s
e
s m
o
c
k
_
f
o
o .
.
.
}
The usage of S
t
r
i
c
t
M
o
c
kis similar, except that it makes all uninteresting calls failures:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
t
r
i
c
t
M
o
c
k
;
T
E
S
T
(
.
.
.
) {
S
t
r
i
c
t
M
o
c
k
<
M
o
c
k
F
o
o
> m
o
c
k
_
f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
f
o
o
, D
o
T
h
i
s
(
)
)
;
.
.
. c
o
d
e t
h
a
t u
s
e
s m
o
c
k
_
f
o
o .
.
.
/
/ T
h
e t
e
s
t w
i
l
l f
a
i
l i
f a m
e
t
h
o
d o
f m
o
c
k
_
f
o
o o
t
h
e
r t
h
a
n D
o
T
h
i
s
(
)
/
/ i
s c
a
l
l
e
d
.
}
There are some caveats though (I don't like them just as much as the next guy, but sadly they are side effects of C++'s limitations):
1. N
i
c
e
M
o
c
k
<
M
o
c
k
F
o
o
>and S
t
r
i
c
t
M
o
c
k
<
M
o
c
k
F
o
o
>only work for mock methods defined using the M
O
C
K
_
M
E
T
H
O
D
*family of macros directly in
the M
o
c
k
F
o
oclass. If a mock method is defined in a base class of M
o
c
k
F
o
o
, the "nice" or "strict" modifier may not affect it, depending on
the compiler. In particular, nesting N
i
c
e
M
o
c
kand S
t
r
i
c
t
M
o
c
k(e.g. N
i
c
e
M
o
c
k
<
S
t
r
i
c
t
M
o
c
k
<
M
o
c
k
F
o
o
> >
) is not supported.
2. The constructors of the base mock (M
o
c
k
F
o
o
) cannot have arguments passed by nonconst reference, which happens to be banned by the
Google C++ style guide.
3. During the constructor or destructor of M
o
c
k
F
o
o
, the mock object is not nice or strict. This may cause surprises if the constructor or
destructor calls a mock method on t
h
i
sobject. (This behavior, however, is consistent with C++'s general rule: if a constructor or destructor
calls a virtual method of t
h
i
sobject, that method is treated as nonvirtual. In other words, to the base class's constructor or destructor,
t
h
i
sobject behaves like an instance of the base class, not the derived class. This rule is required for safety. Otherwise a base constructor
may use members of a derived class before they are initialized, or a base destructor may use members of a derived class after they have
been destroyed.)
Finally, you should be very cautious about when to use naggy or strict mocks, as they tend to make tests more brittle and harder to maintain.
When you refactor your code without changing its externally visible behavior, ideally you should't need to update any tests. If your code interacts
with a naggy mock, however, you may start to get spammed with warnings as the result of your change. Worse, if your code interacts with a
strict mock, your tests may start to fail and you'll be forced to fix them. Our general recommendation is to use nice mocks (not yet the default)
most of the time, use naggy mocks (the current default) when developing or debugging tests, and use strict mocks only as the last resort.

Simplifying the Interface without Breaking Existing Code
Sometimes a method has a long list of arguments that is mostly uninteresting. For example,
c
l
a
s
s L
o
g
S
i
n
k {
p
u
b
l
i
c
:
.
.
.
v
i
r
t
u
a
l v
o
i
d s
e
n
d
(
L
o
g
S
e
v
e
r
i
t
y s
e
v
e
r
i
t
y
, c
o
n
s
t c
h
a
r
* f
u
l
l
_
f
i
l
e
n
a
m
e
,
c
o
n
s
t c
h
a
r
* b
a
s
e
_
f
i
l
e
n
a
m
e
, i
n
t l
i
n
e
,
c
o
n
s
t s
t
r
u
c
t t
m
* t
m
_
t
i
m
e
,
c
o
n
s
t c
h
a
r
* m
e
s
s
a
g
e
, s
i
z
e
_
t m
e
s
s
a
g
e
_
l
e
n
) = 0
;
}
;
This method's argument list is lengthy and hard to work with (let's say that the m
e
s
s
a
g
eargument is not even 0terminated). If we mock it as is,
using the mock will be awkward. If, however, we try to simplify this interface, we'll need to fix all clients depending on it, which is often
infeasible.
The trick is to redispatch the method in the mock class:
c
l
a
s
s S
c
o
p
e
d
M
o
c
k
L
o
g : p
u
b
l
i
c L
o
g
S
i
n
k {
p
u
b
l
i
c
:
.
.
.
v
i
r
t
u
a
l v
o
i
d s
e
n
d
(
L
o
g
S
e
v
e
r
i
t
y s
e
v
e
r
i
t
y
, c
o
n
s
t c
h
a
r
* f
u
l
l
_
f
i
l
e
n
a
m
e
,
c
o
n
s
t c
h
a
r
* b
a
s
e
_
f
i
l
e
n
a
m
e
, i
n
t l
i
n
e
, c
o
n
s
t t
m
* t
m
_
t
i
m
e
,
c
o
n
s
t c
h
a
r
* m
e
s
s
a
g
e
, s
i
z
e
_
t m
e
s
s
a
g
e
_
l
e
n
) {
/
/ W
e a
r
e o
n
l
y i
n
t
e
r
e
s
t
e
d i
n t
h
e l
o
g s
e
v
e
r
i
t
y
, f
u
l
l f
i
l
e n
a
m
e
, a
n
d
/
/ l
o
g m
e
s
s
a
g
e
.
L
o
g
(
s
e
v
e
r
i
t
y
, f
u
l
l
_
f
i
l
e
n
a
m
e
, s
t
d
:
:
s
t
r
i
n
g
(
m
e
s
s
a
g
e
, m
e
s
s
a
g
e
_
l
e
n
)
)
;
}
/
/ I
m
p
l
e
m
e
n
t
s t
h
e m
o
c
k m
e
t
h
o
d
:
/
/
/
/ v
o
i
d L
o
g
(
L
o
g
S
e
v
e
r
i
t
y s
e
v
e
r
i
t
y
,
/
/ c
o
n
s
t s
t
r
i
n
g
& f
i
l
e
_
p
a
t
h
,
/
/ c
o
n
s
t s
t
r
i
n
g
& m
e
s
s
a
g
e
)
;
M
O
C
K
_
M
E
T
H
O
D
3
(
L
o
g
, v
o
i
d
(
L
o
g
S
e
v
e
r
i
t
y s
e
v
e
r
i
t
y
, c
o
n
s
t s
t
r
i
n
g
& f
i
l
e
_
p
a
t
h
,
c
o
n
s
t s
t
r
i
n
g
& m
e
s
s
a
g
e
)
)
;
}
;
By defining a new mock method with a trimmed argument list, we make the mock class much more userfriendly.
Alternative to Mocking Concrete Classes
Often you may find yourself using classes that don't implement interfaces. In order to test your code that uses such a class (let's call it
C
o
n
c
r
e
t
e
), you may be tempted to make the methods of C
o
n
c
r
e
t
evirtual and then mock it.
Try not to do that.
Making a nonvirtual function virtual is a big decision. It creates an extension point where subclasses can tweak your class' behavior. This
weakens your control on the class because now it's harder to maintain the class' invariants. You should make a function virtual only when there
is a valid reason for a subclass to override it.
Mocking concrete classes directly is problematic as it creates a tight coupling between the class and the tests any small change in the class
may invalidate your tests and make test maintenance a pain.
To avoid such problems, many programmers have been practicing "coding to interfaces": instead of talking to the C
o
n
c
r
e
t
eclass, your code
would define an interface and talk to it. Then you implement that interface as an adaptor on top of C
o
n
c
r
e
t
e
. In tests, you can easily mock that
interface to observe how your code is doing.
This technique incurs some overhead:
You pay the cost of virtual function calls (usually not a problem).
There is more abstraction for the programmers to learn.
However, it can also bring significant benefits in addition to better testability:
C
o
n
c
r
e
t
e
's API may not fit your problem domain very well, as you may not be the only client it tries to serve. By designing your own
interface, you have a chance to tailor it to your need you may add higherlevel functionalities, rename stuff, etc instead of just trimming the
class. This allows you to write your code (user of the interface) in a more natural way, which means it will be more readable, more
maintainable, and you'll be more productive.
If C
o
n
c
r
e
t
e
's implementation ever has to change, you don't have to rewrite everywhere it is used. Instead, you can absorb the change in
your implementation of the interface, and your other code and tests will be insulated from this change.

Some people worry that if everyone is practicing this technique, they will end up writing lots of redundant code. This concern is totally
understandable. However, there are two reasons why it may not be the case:
Different projects may need to use C
o
n
c
r
e
t
ein different ways, so the best interfaces for them will be different. Therefore, each of them will
have its own domainspecific interface on top of C
o
n
c
r
e
t
e
, and they will not be the same code.
If enough projects want to use the same interface, they can always share it, just like they have been sharing C
o
n
c
r
e
t
e
. You can check in
the interface and the adaptor somewhere near C
o
n
c
r
e
t
e(perhaps in a c
o
n
t
r
i
bsubdirectory) and let many projects use it.
You need to weigh the pros and cons carefully for your particular problem, but I'd like to assure you that the Java community has been practicing
this for a long time and it's a proven effective technique applicable in a wide variety of situations. :)
Delegating Calls to a Fake
Some times you have a nontrivial fake implementation of an interface. For example:
c
l
a
s
s F
o
o {
p
u
b
l
i
c
:
v
i
r
t
u
a
l ~
F
o
o
(
) {
}
v
i
r
t
u
a
l c
h
a
r D
o
T
h
i
s
(
i
n
t n
) = 0
;
v
i
r
t
u
a
l v
o
i
d D
o
T
h
a
t
(
c
o
n
s
t c
h
a
r
* s
, i
n
t
* p
) = 0
;
}
;
c
l
a
s
s F
a
k
e
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
v
i
r
t
u
a
l c
h
a
r D
o
T
h
i
s
(
i
n
t n
) {
r
e
t
u
r
n (
n > 0
) ? '
+
' :
(
n < 0
) ? '
-
' : '
0
'
;
}
v
i
r
t
u
a
l v
o
i
d D
o
T
h
a
t
(
c
o
n
s
t c
h
a
r
* s
, i
n
t
* p
) {
*
p = s
t
r
l
e
n
(
s
)
;
}
}
;
Now you want to mock this interface such that you can set expectations on it. However, you also want to use F
a
k
e
F
o
ofor the default behavior,
as duplicating it in the mock object is, well, a lot of work.
When you define the mock class using Google Mock, you can have it delegate its default action to a fake class you already have, using this
pattern:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
/
/ N
o
r
m
a
l m
o
c
k m
e
t
h
o
d d
e
f
i
n
i
t
i
o
n
s u
s
i
n
g G
o
o
g
l
e M
o
c
k
.
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
i
s
, c
h
a
r
(
i
n
t n
)
)
;
M
O
C
K
_
M
E
T
H
O
D
2
(
D
o
T
h
a
t
, v
o
i
d
(
c
o
n
s
t c
h
a
r
* s
, i
n
t
* p
)
)
;
/
/ D
e
l
e
g
a
t
e
s t
h
e d
e
f
a
u
l
t a
c
t
i
o
n
s o
f t
h
e m
e
t
h
o
d
s t
o a F
a
k
e
F
o
o o
b
j
e
c
t
.
/
/ T
h
i
s m
u
s
t b
e c
a
l
l
e
d *
b
e
f
o
r
e
* t
h
e c
u
s
t
o
m O
N
_
C
A
L
L
(
) s
t
a
t
e
m
e
n
t
s
.
v
o
i
d D
e
l
e
g
a
t
e
T
o
F
a
k
e
(
) {
O
N
_
C
A
L
L
(
*
t
h
i
s
, D
o
T
h
i
s
(
_
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
I
n
v
o
k
e
(
&
f
a
k
e
_
, &
F
a
k
e
F
o
o
:
:
D
o
T
h
i
s
)
)
;
O
N
_
C
A
L
L
(
*
t
h
i
s
, D
o
T
h
a
t
(
_
, _
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
I
n
v
o
k
e
(
&
f
a
k
e
_
, &
F
a
k
e
F
o
o
:
:
D
o
T
h
a
t
)
)
;
}
p
r
i
v
a
t
e
:
F
a
k
e
F
o
o f
a
k
e
_
; /
/ K
e
e
p
s a
n i
n
s
t
a
n
c
e o
f t
h
e f
a
k
e i
n t
h
e m
o
c
k
.
}
;
With that, you can use M
o
c
k
F
o
oin your tests as usual. Just remember that if you don't explicitly set an action in an O
N
_
C
A
L
L
(
)or
E
X
P
E
C
T
_
C
A
L
L
(
)
, the fake will be called upon to do it:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
T
E
S
T
(
A
b
c
T
e
s
t
, X
y
z
) {
M
o
c
k
F
o
o f
o
o
;
f
o
o
.
D
e
l
e
g
a
t
e
T
o
F
a
k
e
(
)
; /
/ E
n
a
b
l
e
s t
h
e f
a
k
e f
o
r d
e
l
e
g
a
t
i
o
n
.
/
/ P
u
t y
o
u
r O
N
_
C
A
L
L
(
f
o
o
, .
.
.
)
s h
e
r
e
, i
f a
n
y
.

/
/ N
o a
c
t
i
o
n s
p
e
c
i
f
i
e
d
, m
e
a
n
i
n
g t
o u
s
e t
h
e d
e
f
a
u
l
t a
c
t
i
o
n
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
5
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
_
, _
)
)
;
i
n
t n = 0
;
E
X
P
E
C
T
_
E
Q
(
'
+
'
, f
o
o
.
D
o
T
h
i
s
(
5
)
)
; /
/ F
a
k
e
F
o
o
:
:
D
o
T
h
i
s
(
) i
s i
n
v
o
k
e
d
.
f
o
o
.
D
o
T
h
a
t
(
"
H
i
"
, &
n
)
; /
/ F
a
k
e
F
o
o
:
:
D
o
T
h
a
t
(
) i
s i
n
v
o
k
e
d
.
E
X
P
E
C
T
_
E
Q
(
2
, n
)
;
}
Some tips:
If you want, you can still override the default action by providing your own O
N
_
C
A
L
L
(
)or using .
W
i
l
l
O
n
c
e
(
)/ .
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
)in
E
X
P
E
C
T
_
C
A
L
L
(
)
.
In D
e
l
e
g
a
t
e
T
o
F
a
k
e
(
)
, you only need to delegate the methods whose fake implementation you intend to use.
The general technique discussed here works for overloaded methods, but you'll need to tell the compiler which version you mean. To
disambiguate a mock function (the one you specify inside the parentheses of O
N
_
C
A
L
L
(
)
), see the "Selecting Between Overloaded
Functions" section on this page; to disambiguate a fake function (the one you place inside I
n
v
o
k
e
(
)
), use a s
t
a
t
i
c
_
c
a
s
tto specify the
function's type. For instance, if class F
o
ohas methods c
h
a
r D
o
T
h
i
s
(
i
n
t n
)and b
o
o
l D
o
T
h
i
s
(
d
o
u
b
l
e x
) c
o
n
s
t
, and you want to invoke
the latter, you need to write I
n
v
o
k
e
(
&
f
a
k
e
_
, s
t
a
t
i
c
_
c
a
s
t

(
&
F
a
k
e
F
o
o
:
:
D
o
T
h
i
s
)
)instead of
I
n
v
o
k
e
(
&
f
a
k
e
_
, &
F
a
k
e
F
o
o
:
:
D
o
T
h
i
s
)(The strangelooking thing inside the angled brackets of s
t
a
t
i
c
_
c
a
s
tis the type of a function
pointer to the second D
o
T
h
i
s
(
)method.).
Having to mix a mock and a fake is often a sign of something gone wrong. Perhaps you haven't got used to the interactionbased way of
testing yet. Or perhaps your interface is taking on too many roles and should be split up. Therefore, don't abuse this. We would only
recommend to do it as an intermediate step when you are refactoring your code.
Regarding the tip on mixing a mock and a fake, here's an example on why it may be a bad sign: Suppose you have a class S
y
s
t
e
mfor lowlevel
system operations. In particular, it does file and I/O operations. And suppose you want to test how your code uses S
y
s
t
e
mto do I/O, and you
just want the file operations to work normally. If you mock out the entire S
y
s
t
e
mclass, you'll have to provide a fake implementation for the file
operation part, which suggests that S
y
s
t
e
mis taking on too many roles.
Instead, you can define a F
i
l
e
O
p
sinterface and an I
O
O
p
sinterface and split S
y
s
t
e
m
's functionalities into the two. Then you can mock I
O
O
p
s
without mocking F
i
l
e
O
p
s
.
Delegating Calls to a Real Object
When using testing doubles (mocks, fakes, stubs, and etc), sometimes their behaviors will differ from those of the real objects. This difference
could be either intentional (as in simulating an error such that you can test the error handling code) or unintentional. If your mocks have different
behaviors than the real objects by mistake, you could end up with code that passes the tests but fails in production.
You can use the delegatingtoreal technique to ensure that your mock has the same behavior as the real object while retaining the ability to
validate calls. This technique is very similar to the delegatingtofake technique, the difference being that we use a real object instead of a fake.
Here's an example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
t
L
e
a
s
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
o
c
k
F
o
o
(
) {
/
/ B
y d
e
f
a
u
l
t
, a
l
l c
a
l
l
s a
r
e d
e
l
e
g
a
t
e
d t
o t
h
e r
e
a
l o
b
j
e
c
t
.
O
N
_
C
A
L
L
(
*
t
h
i
s
, D
o
T
h
i
s
(
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
I
n
v
o
k
e
(
&
r
e
a
l
_
, &
F
o
o
:
:
D
o
T
h
i
s
)
)
;
O
N
_
C
A
L
L
(
*
t
h
i
s
, D
o
T
h
a
t
(
_
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
I
n
v
o
k
e
(
&
r
e
a
l
_
, &
F
o
o
:
:
D
o
T
h
a
t
)
)
;
.
.
.
}
M
O
C
K
_
M
E
T
H
O
D
0
(
D
o
T
h
i
s
, .
.
.
)
;
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
a
t
, .
.
.
)
;
.
.
.
p
r
i
v
a
t
e
:
F
o
o r
e
a
l
_
;
}
;
.
.
.
M
o
c
k
F
o
o m
o
c
k
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, D
o
T
h
i
s
(
)
)
.
T
i
m
e
s
(
3
)
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, D
o
T
h
a
t
(
"
H
i
"
)
)

E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, D
o
T
h
a
t
(
"
H
i
"
)
)
.
T
i
m
e
s
(
A
t
L
e
a
s
t
(
1
)
)
;
.
.
. u
s
e m
o
c
k i
n t
e
s
t .
.
.
With this, Google Mock will verify that your code made the right calls (with the right arguments, in the right order, called the right number of
times, etc), and a real object will answer the calls (so the behavior will be the same as in production). This gives you the best of both worlds.
Delegating Calls to a Parent Class
Ideally, you should code to interfaces, whose methods are all pure virtual. In reality, sometimes you do need to mock a virtual method that is not
pure (i.e, it already has an implementation). For example:
c
l
a
s
s F
o
o {
p
u
b
l
i
c
:
v
i
r
t
u
a
l ~
F
o
o
(
)
;
v
i
r
t
u
a
l v
o
i
d P
u
r
e
(
i
n
t n
) = 0
;
v
i
r
t
u
a
l i
n
t C
o
n
c
r
e
t
e
(
c
o
n
s
t c
h
a
r
* s
t
r
) { .
.
. }
}
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
/
/ M
o
c
k
i
n
g a p
u
r
e m
e
t
h
o
d
.
M
O
C
K
_
M
E
T
H
O
D
1
(
P
u
r
e
, v
o
i
d
(
i
n
t n
)
)
;
/
/ M
o
c
k
i
n
g a c
o
n
c
r
e
t
e m
e
t
h
o
d
. F
o
o
:
:
C
o
n
c
r
e
t
e
(
) i
s s
h
a
d
o
w
e
d
.
M
O
C
K
_
M
E
T
H
O
D
1
(
C
o
n
c
r
e
t
e
, i
n
t
(
c
o
n
s
t c
h
a
r
* s
t
r
)
)
;
}
;
Sometimes you may want to call F
o
o
:
:
C
o
n
c
r
e
t
e
(
)instead of M
o
c
k
F
o
o
:
:
C
o
n
c
r
e
t
e
(
)
. Perhaps you want to do it as part of a stub action, or
perhaps your test doesn't need to mock C
o
n
c
r
e
t
e
(
)at all (but it would be ohso painful to have to define a new mock class whenever you don't
need to mock one of its methods).
The trick is to leave a back door in your mock class for accessing the real methods in the base class:
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
/
/ M
o
c
k
i
n
g a p
u
r
e m
e
t
h
o
d
.
M
O
C
K
_
M
E
T
H
O
D
1
(
P
u
r
e
, v
o
i
d
(
i
n
t n
)
)
;
/
/ M
o
c
k
i
n
g a c
o
n
c
r
e
t
e m
e
t
h
o
d
. F
o
o
:
:
C
o
n
c
r
e
t
e
(
) i
s s
h
a
d
o
w
e
d
.
M
O
C
K
_
M
E
T
H
O
D
1
(
C
o
n
c
r
e
t
e
, i
n
t
(
c
o
n
s
t c
h
a
r
* s
t
r
)
)
;
/
/ U
s
e t
h
i
s t
o c
a
l
l C
o
n
c
r
e
t
e
(
) d
e
f
i
n
e
d i
n F
o
o
.
i
n
t F
o
o
C
o
n
c
r
e
t
e
(
c
o
n
s
t c
h
a
r
* s
t
r
) { r
e
t
u
r
n F
o
o
:
:
C
o
n
c
r
e
t
e
(
s
t
r
)
; }
}
;
Now, you can call F
o
o
:
:
C
o
n
c
r
e
t
e
(
)inside an action by:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, C
o
n
c
r
e
t
e
(
_
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
&
f
o
o
, &
M
o
c
k
F
o
o
:
:
F
o
o
C
o
n
c
r
e
t
e
)
)
;
or tell the mock object that you don't want to mock C
o
n
c
r
e
t
e
(
)
:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
.
.
.
O
N
_
C
A
L
L
(
f
o
o
, C
o
n
c
r
e
t
e
(
_
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
I
n
v
o
k
e
(
&
f
o
o
, &
M
o
c
k
F
o
o
:
:
F
o
o
C
o
n
c
r
e
t
e
)
)
;
(Why don't we just write I
n
v
o
k
e
(
&
f
o
o
, &
F
o
o
:
:
C
o
n
c
r
e
t
e
)
? If you do that, M
o
c
k
F
o
o
:
:
C
o
n
c
r
e
t
e
(
)will be called (and cause an infinite recursion)
since F
o
o
:
:
C
o
n
c
r
e
t
e
(
)is virtual. That's just how C++ works.)
Using Matchers
Matching Argument Values Exactly
You can specify exactly which arguments a mock method is expecting:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
5
)
)

.
W
i
l
l
O
n
c
e
(
R
e
t
u
r
n
(
'
a
'
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
"
H
e
l
l
o
"
, b
a
r
)
)
;
Using Simple Matchers
You can use matchers to match arguments that have a certain property:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
o
t
N
u
l
l
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
G
e
(
5
)
)
) /
/ T
h
e a
r
g
u
m
e
n
t m
u
s
t b
e >
= 5
.
.
W
i
l
l
O
n
c
e
(
R
e
t
u
r
n
(
'
a
'
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
"
H
e
l
l
o
"
, N
o
t
N
u
l
l
(
)
)
)
;
/
/ T
h
e s
e
c
o
n
d a
r
g
u
m
e
n
t m
u
s
t n
o
t b
e N
U
L
L
.
A frequently used matcher is _
, which matches anything:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
o
t
N
u
l
l
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
_
, N
o
t
N
u
l
l
(
)
)
)
;
Combining Matchers
You can build complex matchers from existing ones using A
l
l
O
f
(
)
, A
n
y
O
f
(
)
, and N
o
t
(
)
:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
l
l
O
f
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
H
a
s
S
u
b
s
t
r
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
o
t
;
.
.
.
/
/ T
h
e a
r
g
u
m
e
n
t m
u
s
t b
e > 5 a
n
d !
= 1
0
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
A
l
l
O
f
(
G
t
(
5
)
,
N
e
(
1
0
)
)
)
)
;
/
/ T
h
e f
i
r
s
t a
r
g
u
m
e
n
t m
u
s
t n
o
t c
o
n
t
a
i
n s
u
b
-
s
t
r
i
n
g "
b
l
a
h
"
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
N
o
t
(
H
a
s
S
u
b
s
t
r
(
"
b
l
a
h
"
)
)
,
N
U
L
L
)
)
;
Casting Matchers
Google Mock matchers are statically typed, meaning that the compiler can catch your mistake if you use a matcher of the wrong type (for
example, if you use E
q
(
5
)to match a s
t
r
i
n
gargument). Good for you!
Sometimes, however, you know what you're doing and want the compiler to give you some slack. One example is that you have a matcher for
l
o
n
gand the argument you want to match is i
n
t
. While the two types aren't exactly the same, there is nothing really wrong with using a
M
a
t
c
h
e
r
<
l
o
n
g
>to match an i
n
t after all, we can first convert the i
n
targument to a l
o
n
gbefore giving it to the matcher.
To support this need, Google Mock gives you the S
a
f
e
M
a
t
c
h
e
r
C
a
s
t
<
T
>
(
m
)function. It casts a matcher mto type M
a
t
c
h
e
r
<
T
>
. To ensure
safety, Google Mock checks that (let Ube the type maccepts):
1. Type Tcan be implicitly cast to type U
;
2. When both Tand Uare builtin arithmetic types (b
o
o
l
, integers, and floatingpoint numbers), the conversion from Tto Uis not lossy (in other
words, any value representable by Tcan also be represented by U
); and
3. When Uis a reference, Tmust also be a reference (as the underlying matcher may be interested in the address of the Uvalue).
The code won't compile if any of these conditions isn't met.
Here's one example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
a
f
e
M
a
t
c
h
e
r
C
a
s
t
;
/
/ A b
a
s
e c
l
a
s
s a
n
d a c
h
i
l
d c
l
a
s
s
.
c
l
a
s
s B
a
s
e { .
.
. }
;
c
l
a
s
s D
e
r
i
v
e
d : p
u
b
l
i
c B
a
s
e { .
.
. }
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
i
s
, v
o
i
d
(
D
e
r
i
v
e
d
* d
e
r
i
v
e
d
)
)
;

}
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
/
/ m i
s a M
a
t
c
h
e
r
 w
e g
o
t f
r
o
m s
o
m
e
w
h
e
r
e
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
S
a
f
e
M
a
t
c
h
e
r
C
a
s
t
<
D
e
r
i
v
e
d
*
>
(
m
)
)
)
;
If you find S
a
f
e
M
a
t
c
h
e
r
C
a
s
t
<
T
>
(
m
)too limiting, you can use a similar function M
a
t
c
h
e
r
C
a
s
t
<
T
>
(
m
)
. The difference is that M
a
t
c
h
e
r
C
a
s
tworks
as long as you can s
t
a
t
i
c
_
c
a
s
ttype Tto type U
.
M
a
t
c
h
e
r
C
a
s
tessentially lets you bypass C++'s type system (s
t
a
t
i
c
_
c
a
s
tisn't always safe as it could throw away information, for example),
so be careful not to misuse/abuse it.
Selecting Between Overloaded Functions
If you expect an overloaded function to be called, the compiler may need some help on which overloaded version it is.
To disambiguate functions overloaded on the constness of this object, use the C
o
n
s
t
(
)argument wrapper.
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
R
e
f
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
.
.
.
M
O
C
K
_
M
E
T
H
O
D
0
(
G
e
t
B
a
r
, B
a
r
&
(
)
)
;
M
O
C
K
_
C
O
N
S
T
_
M
E
T
H
O
D
0
(
G
e
t
B
a
r
, c
o
n
s
t B
a
r
&
(
)
)
;
}
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
B
a
r b
a
r
1
, b
a
r
2
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, G
e
t
B
a
r
(
)
) /
/ T
h
e n
o
n
-
c
o
n
s
t G
e
t
B
a
r
(
)
.
.
W
i
l
l
O
n
c
e
(
R
e
t
u
r
n
R
e
f
(
b
a
r
1
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
C
o
n
s
t
(
f
o
o
)
, G
e
t
B
a
r
(
)
) /
/ T
h
e c
o
n
s
t G
e
t
B
a
r
(
)
.
.
W
i
l
l
O
n
c
e
(
R
e
t
u
r
n
R
e
f
(
b
a
r
2
)
)
;
(C
o
n
s
t
(
)is defined by Google Mock and returns a c
o
n
s
treference to its argument.)
To disambiguate overloaded functions with the same number of arguments but different argument types, you may need to specify the exact type
of a matcher, either by wrapping your matcher in M
a
t
c
h
e
r
<
t
y
p
e
>
(
)
, or using a matcher whose type is fixed (T
y
p
e
d
E
q
<
t
y
p
e
>
, A
n
<
t
y
p
e
>
(
)
, etc):
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
n
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
M
a
t
c
h
e
r
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
T
y
p
e
d
E
q
;
c
l
a
s
s M
o
c
k
P
r
i
n
t
e
r : p
u
b
l
i
c P
r
i
n
t
e
r {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
P
r
i
n
t
, v
o
i
d
(
i
n
t n
)
)
;
M
O
C
K
_
M
E
T
H
O
D
1
(
P
r
i
n
t
, v
o
i
d
(
c
h
a
r c
)
)
;
}
;
T
E
S
T
(
P
r
i
n
t
e
r
T
e
s
t
, P
r
i
n
t
) {
M
o
c
k
P
r
i
n
t
e
r p
r
i
n
t
e
r
;
E
X
P
E
C
T
_
C
A
L
L
(
p
r
i
n
t
e
r
, P
r
i
n
t
(
A
n

(
)
)
)
; /
/ v
o
i
d P
r
i
n
t
(
i
n
t
)
;
E
X
P
E
C
T
_
C
A
L
L
(
p
r
i
n
t
e
r
, P
r
i
n
t
(
M
a
t
c
h
e
r

(
L
t
(
5
)
)
)
)
; /
/ v
o
i
d P
r
i
n
t
(
i
n
t
)
;
E
X
P
E
C
T
_
C
A
L
L
(
p
r
i
n
t
e
r
, P
r
i
n
t
(
T
y
p
e
d
E
q
<
c
h
a
r
>
(
'
a
'
)
)
)
; /
/ v
o
i
d P
r
i
n
t
(
c
h
a
r
)
;
p
r
i
n
t
e
r
.
P
r
i
n
t
(
3
)
;
p
r
i
n
t
e
r
.
P
r
i
n
t
(
6
)
;
p
r
i
n
t
e
r
.
P
r
i
n
t
(
'
a
'
)
;
}
Performing Different Actions Based on the Arguments
When a mock method is called, the last matching expectation that's still active will be selected (think "newer overrides older"). So, you can
make a method do different things depending on its argument values like this:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
.
.
.
/
/ T
h
e d
e
f
a
u
l
t c
a
s
e
.

/
/ T
h
e d
e
f
a
u
l
t c
a
s
e
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
_
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
(
'
b
'
)
)
;
/
/ T
h
e m
o
r
e s
p
e
c
i
f
i
c c
a
s
e
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
L
t
(
5
)
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
(
'
a
'
)
)
;
Now, if f
o
o
.
D
o
T
h
i
s
(
)is called with a value less than 5, '
a
'will be returned; otherwise '
b
'will be returned.
Matching Multiple Arguments as a Whole
Sometimes it's not enough to match the arguments individually. For example, we may want to say that the first argument must be less than the
second argument. The W
i
t
h
(
)clause allows us to match all arguments of a mock function as a whole. For example,
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
e
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, I
n
R
a
n
g
e
(
N
e
(
0
)
, _
)
)
.
W
i
t
h
(
L
t
(
)
)
;
says that the first argument of I
n
R
a
n
g
e
(
)must not be 0, and must be less than the second argument.
The expression inside W
i
t
h
(
)must be a matcher of type M
a
t
c
h
e
r
<
t
r
1
:
:
t
u
p
l
e
<
A
1
, .
.
.
, A
n
> >
, where A
1
, ..., A
nare the types of the function
arguments.
You can also write A
l
l
A
r
g
s
(
m
)instead of minside .
W
i
t
h
(
)
. The two forms are equivalent, but .
W
i
t
h
(
A
l
l
A
r
g
s
(
L
t
(
)
)
)is more readable than
.
W
i
t
h
(
L
t
(
)
)
.
You can use A
r
g
s
<
k
1
, .
.
.
, k
n
>
(
m
)to match the nselected arguments (as a tuple) against m
. For example,
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
l
l
O
f
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
r
g
s
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
t
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
l
a
h
(
_
, _
, _
)
)
.
W
i
t
h
(
A
l
l
O
f
(
A
r
g
s
<
0
, 1
>
(
L
t
(
)
)
, A
r
g
s
<
1
, 2
>
(
L
t
(
)
)
)
)
;
says that B
l
a
h
(
)will be called with arguments x
, y
, and zwhere x < y < z
.
As a convenience and example, Google Mock provides some matchers for 2tuples, including the L
t
(
)matcher above. See the CheatSheet for
the complete list.
Note that if you want to pass the arguments to a predicate of your own (e.g. .
W
i
t
h
(
A
r
g
s
<
0
, 1
>
(
T
r
u
l
y
(
&
M
y
P
r
e
d
i
c
a
t
e
)
)
)
), that predicate
MUST be written to take a t
r
1
:
:
t
u
p
l
eas its argument; Google Mock will pass the nselected arguments as one single tuple to the predicate.
Using Matchers as Predicates
Have you noticed that a matcher is just a fancy predicate that also knows how to describe itself? Many existing algorithms take predicates as
arguments (e.g. those defined in STL's <
a
l
g
o
r
i
t
h
m
>header), and it would be a shame if Google Mock matchers are not allowed to participate.
Luckily, you can use a matcher where a unary predicate functor is expected by wrapping it inside the M
a
t
c
h
e
s
(
)function. For example,
#
i
n
c
l
u
d
e <
a
l
g
o
r
i
t
h
m
>
#
i
n
c
l
u
d
e <
v
e
c
t
o
r
>
s
t
d
:
:
v
e
c
t
o
r
 v
;
.
.
.
/
/ H
o
w m
a
n
y e
l
e
m
e
n
t
s i
n v a
r
e >
= 1
0
?
c
o
n
s
t i
n
t c
o
u
n
t = c
o
u
n
t
_
i
f
(
v
.
b
e
g
i
n
(
)
, v
.
e
n
d
(
)
, M
a
t
c
h
e
s
(
G
e
(
1
0
)
)
)
;
Since you can build complex matchers from simpler ones easily using Google Mock, this gives you a way to conveniently construct composite
predicates (doing the same using STL's <
f
u
n
c
t
i
o
n
a
l
>header is just painful). For example, here's a predicate that's satisfied by any number that
is >= 0, <= 100, and != 50:
M
a
t
c
h
e
s
(
A
l
l
O
f
(
G
e
(
0
)
, L
e
(
1
0
0
)
, N
e
(
5
0
)
)
)
Using Matchers in Google Test Assertions
Since matchers are basically predicates that also know how to describe themselves, there is a way to take advantage of them in Google Test
assertions. It's called A
S
S
E
R
T
_
T
H
A
Tand E
X
P
E
C
T
_
T
H
A
T
:

A
S
S
E
R
T
_
T
H
A
T
(
v
a
l
u
e
, m
a
t
c
h
e
r
)
; /
/ A
s
s
e
r
t
s t
h
a
t v
a
l
u
e m
a
t
c
h
e
s m
a
t
c
h
e
r
.
E
X
P
E
C
T
_
T
H
A
T
(
v
a
l
u
e
, m
a
t
c
h
e
r
)
; /
/ T
h
e n
o
n
-
f
a
t
a
l v
e
r
s
i
o
n
.
For example, in a Google Test test you can write:
#
i
n
c
l
u
d
e "
g
m
o
c
k
/
g
m
o
c
k
.
h
"
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
l
l
O
f
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
M
a
t
c
h
e
s
R
e
g
e
x
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
t
a
r
t
s
W
i
t
h
;
.
.
.
E
X
P
E
C
T
_
T
H
A
T
(
F
o
o
(
)
, S
t
a
r
t
s
W
i
t
h
(
"
H
e
l
l
o
"
)
)
;
E
X
P
E
C
T
_
T
H
A
T
(
B
a
r
(
)
, M
a
t
c
h
e
s
R
e
g
e
x
(
"
L
i
n
e

d
+
"
)
)
;
A
S
S
E
R
T
_
T
H
A
T
(
B
a
z
(
)
, A
l
l
O
f
(
G
e
(
5
)
, L
e
(
1
0
)
)
)
;
which (as you can probably guess) executes F
o
o
(
)
, B
a
r
(
)
, and B
a
z
(
)
, and verifies that:
F
o
o
(
)returns a string that starts with "
H
e
l
l
o
"
.
B
a
r
(
)returns a string that matches regular expression "
L
i
n
e

d
+
"
.
B
a
z
(
)returns a number in the range [5, 10].
The nice thing about these macros is that they read like English. They generate informative messages too. For example, if the first
E
X
P
E
C
T
_
T
H
A
T
(
)above fails, the message will be something like:
V
a
l
u
e o
f
: F
o
o
(
)
A
c
t
u
a
l
: "
H
i
, w
o
r
l
d
!
"
E
x
p
e
c
t
e
d
: s
t
a
r
t
s w
i
t
h "
H
e
l
l
o
"
Credit: The idea of (
A
S
S
E
R
T
|
E
X
P
E
C
T
)
_
T
H
A
Twas stolen from the Hamcrest project, which adds a
s
s
e
r
t
T
h
a
t
(
)to JUnit.
Using Predicates as Matchers
Google Mock provides a builtin set of matchers. In case you find them lacking, you can use an arbitray unary predicate function or functor as a
matcher as long as the predicate accepts a value of the type you want. You do this by wrapping the predicate inside the T
r
u
l
y
(
)function, for
example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
T
r
u
l
y
;
i
n
t I
s
E
v
e
n
(
i
n
t n
) { r
e
t
u
r
n (
n % 2
) =
= 0 ? 1 : 0
; }
.
.
.
/
/ B
a
r
(
) m
u
s
t b
e c
a
l
l
e
d w
i
t
h a
n e
v
e
n n
u
m
b
e
r
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
T
r
u
l
y
(
I
s
E
v
e
n
)
)
)
;
Note that the predicate function / functor doesn't have to return b
o
o
l
. It works as long as the return value can be used as the condition in
statement i
f (
c
o
n
d
i
t
i
o
n
) .
.
.
.
Matching Arguments that Are Not Copyable
When you do an E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
o
b
j
, F
o
o
(
b
a
r
)
)
, Google Mock saves away a copy of b
a
r
. When F
o
o
(
)is called later, Google Mock
compares the argument to F
o
o
(
)with the saved copy of b
a
r
. This way, you don't need to worry about b
a
rbeing modified or destroyed after the
E
X
P
E
C
T
_
C
A
L
L
(
)is executed. The same is true when you use matchers like E
q
(
b
a
r
)
, L
e
(
b
a
r
)
, and so on.
But what if b
a
rcannot be copied (i.e. has no copy constructor)? You could define your own matcher function and use it with T
r
u
l
y
(
)
, as the
previous couple of recipes have shown. Or, you may be able to get away from it if you can guarantee that b
a
rwon't be changed after the
E
X
P
E
C
T
_
C
A
L
L
(
)is executed. Just tell Google Mock that it should save a reference to b
a
r
, instead of a copy of it. Here's how:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
E
q
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
B
y
R
e
f
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
L
t
;
.
.
.
/
/ E
x
p
e
c
t
s t
h
a
t F
o
o
(
)
'
s a
r
g
u
m
e
n
t =
= b
a
r
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
o
b
j
, F
o
o
(
E
q
(
B
y
R
e
f
(
b
a
r
)
)
)
)
;
/
/ E
x
p
e
c
t
s t
h
a
t F
o
o
(
)
'
s a
r
g
u
m
e
n
t < b
a
r
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
_
o
b
j
, F
o
o
(
L
t
(
B
y
R
e
f
(
b
a
r
)
)
)
)
;

Remember: if you do this, don't change b
a
rafter the E
X
P
E
C
T
_
C
A
L
L
(
)
, or the result is undefined.
Validating a Member of an Object
Often a mock function takes a reference to object as an argument. When matching the argument, you may not want to compare the entire object
against a fixed object, as that may be overspecification. Instead, you may need to validate a certain member variable or the result of a certain
getter method of the object. You can do this with F
i
e
l
d
(
)and P
r
o
p
e
r
t
y
(
)
. More specifically,
F
i
e
l
d
(
&
F
o
o
:
:
b
a
r
, m
)
is a matcher that matches a F
o
oobject whose b
a
rmember variable satisfies matcher m
.
P
r
o
p
e
r
t
y
(
&
F
o
o
:
:
b
a
z
, m
)
is a matcher that matches a F
o
oobject whose b
a
z
(
)method returns a value that satisfies matcher m
.
For example:
F
i
e
l
d
(
&
F
o
o
:
:
n
u
m
b
e
r
, G
e
(
3
)
) Matches xwhere x
.
n
u
m
b
e
r >
= 3
.
P
r
o
p
e
r
t
y
(
&
F
o
o
:
:
n
a
m
e
, S
t
a
r
t
s
W
i
t
h
(
"
J
o
h
n "
)
) Matches xwhere x
.
n
a
m
e
(
)starts with "
J
o
h
n "
.
Note that in P
r
o
p
e
r
t
y
(
&
F
o
o
:
:
b
a
z
, .
.
.
)
, method b
a
z
(
)must take no argument and be declared as c
o
n
s
t
.
BTW, F
i
e
l
d
(
)and P
r
o
p
e
r
t
y
(
)can also match plain pointers to objects. For instance,
F
i
e
l
d
(
&
F
o
o
:
:
n
u
m
b
e
r
, G
e
(
3
)
)
matches a plain pointer pwhere p
-
>
n
u
m
b
e
r >
= 3
. If pis N
U
L
L
, the match will always fail regardless of the inner matcher.
What if you want to validate more than one members at the same time? Remember that there is A
l
l
O
f
(
)
.
Validating the Value Pointed to by a Pointer Argument
C++ functions often take pointers as arguments. You can use matchers like I
s
N
u
l
l
(
)
, N
o
t
N
u
l
l
(
)
, and other comparison matchers to match a
pointer, but what if you want to make sure the value pointed to by the pointer, instead of the pointer itself, has a certain property? Well, you can
use the P
o
i
n
t
e
e
(
m
)matcher.
P
o
i
n
t
e
e
(
m
)matches a pointer iff mmatches the value the pointer points to. For example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
P
o
i
n
t
e
e
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
P
o
i
n
t
e
e
(
G
e
(
3
)
)
)
)
;
expects f
o
o
.
B
a
r
(
)to be called with a pointer that points to a value greater than or equal to 3.
One nice thing about P
o
i
n
t
e
e
(
)is that it treats a N
U
L
Lpointer as a match failure, so you can write P
o
i
n
t
e
e
(
m
)instead of
A
l
l
O
f
(
N
o
t
N
u
l
l
(
)
, P
o
i
n
t
e
e
(
m
)
)
without worrying that a N
U
L
Lpointer will crash your test.
Also, did we tell you that P
o
i
n
t
e
e
(
)works with both raw pointers and smart pointers (l
i
n
k
e
d
_
p
t
r
, s
h
a
r
e
d
_
p
t
r
, s
c
o
p
e
d
_
p
t
r
, and etc)?
What if you have a pointer to pointer? You guessed it you can use nested P
o
i
n
t
e
e
(
)to probe deeper inside the value. For example,
P
o
i
n
t
e
e
(
P
o
i
n
t
e
e
(
L
t
(
3
)
)
)matches a pointer that points to a pointer that points to a number less than 3 (what a mouthful...).
Testing a Certain Property of an Object
Sometimes you want to specify that an object argument has a certain property, but there is no existing matcher that does this. If you want good
error messages, you should define a matcher. If you want to do it quick and dirty, you could get away with writing an ordinary function.
Let's say you have a mock function that takes an object of type F
o
o
, which has an i
n
t b
a
r
(
)method and an i
n
t b
a
z
(
)method, and you want
to constrain that the argument's b
a
r
(
)value plus its b
a
z
(
)value is a given number. Here's how you can define a matcher to do it:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
M
a
t
c
h
e
r
I
n
t
e
r
f
a
c
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
M
a
t
c
h
R
e
s
u
l
t
L
i
s
t
e
n
e
r
;
c
l
a
s
s B
a
r
P
l
u
s
B
a
z
E
q
M
a
t
c
h
e
r : p
u
b
l
i
c M
a
t
c
h
e
r
I
n
t
e
r
f
a
c
e
<
c
o
n
s
t F
o
o
&
> {
p
u
b
l
i
c
:

p
u
b
l
i
c
:
e
x
p
l
i
c
i
t B
a
r
P
l
u
s
B
a
z
E
q
M
a
t
c
h
e
r
(
i
n
t e
x
p
e
c
t
e
d
_
s
u
m
)
: e
x
p
e
c
t
e
d
_
s
u
m
_
(
e
x
p
e
c
t
e
d
_
s
u
m
) {
}
v
i
r
t
u
a
l b
o
o
l M
a
t
c
h
A
n
d
E
x
p
l
a
i
n
(
c
o
n
s
t F
o
o
& f
o
o
,
M
a
t
c
h
R
e
s
u
l
t
L
i
s
t
e
n
e
r
* l
i
s
t
e
n
e
r
) c
o
n
s
t {
r
e
t
u
r
n (
f
o
o
.
b
a
r
(
) + f
o
o
.
b
a
z
(
)
) =
= e
x
p
e
c
t
e
d
_
s
u
m
_
;
}
v
i
r
t
u
a
l v
o
i
d D
e
s
c
r
i
b
e
T
o
(
:
:
s
t
d
:
:
o
s
t
r
e
a
m
* o
s
) c
o
n
s
t {
*
o
s <
< "
b
a
r
(
) + b
a
z
(
) e
q
u
a
l
s " <
< e
x
p
e
c
t
e
d
_
s
u
m
_
;
}
v
i
r
t
u
a
l v
o
i
d D
e
s
c
r
i
b
e
N
e
g
a
t
i
o
n
T
o
(
:
:
s
t
d
:
:
o
s
t
r
e
a
m
* o
s
) c
o
n
s
t {
*
o
s <
< "
b
a
r
(
) + b
a
z
(
) d
o
e
s n
o
t e
q
u
a
l " <
< e
x
p
e
c
t
e
d
_
s
u
m
_
;
}
p
r
i
v
a
t
e
:
c
o
n
s
t i
n
t e
x
p
e
c
t
e
d
_
s
u
m
_
;
}
;
i
n
l
i
n
e M
a
t
c
h
e
r
<
c
o
n
s
t F
o
o
&
> B
a
r
P
l
u
s
B
a
z
E
q
(
i
n
t e
x
p
e
c
t
e
d
_
s
u
m
) {
r
e
t
u
r
n M
a
k
e
M
a
t
c
h
e
r
(
n
e
w B
a
r
P
l
u
s
B
a
z
E
q
M
a
t
c
h
e
r
(
e
x
p
e
c
t
e
d
_
s
u
m
)
)
;
}
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
.
.
.
, D
o
T
h
i
s
(
B
a
r
P
l
u
s
B
a
z
E
q
(
5
)
)
)
.
.
.
;
Matching Containers
Sometimes an STL container (e.g. list, vector, map, ...) is passed to a mock function and you may want to validate it. Since most STL
containers support the =
=operator, you can write E
q
(
e
x
p
e
c
t
e
d
_
c
o
n
t
a
i
n
e
r
)or simply e
x
p
e
c
t
e
d
_
c
o
n
t
a
i
n
e
rto match a container exactly.
Sometimes, though, you may want to be more flexible (for example, the first element must be an exact match, but the second element can be
any positive number, and so on). Also, containers used in tests often have a small number of elements, and having to define the expected
container outofline is a bit of a hassle.
You can use the E
l
e
m
e
n
t
s
A
r
e
(
)or U
n
o
r
d
e
r
e
d
E
l
e
m
e
n
t
s
A
r
e
(
)matcher in such cases:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
E
l
e
m
e
n
t
s
A
r
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
t
;
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
F
o
o
, v
o
i
d
(
c
o
n
s
t v
e
c
t
o
r

& n
u
m
b
e
r
s
)
)
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
E
l
e
m
e
n
t
s
A
r
e
(
1
, G
t
(
0
)
, _
, 5
)
)
)
;
The above matcher says that the container must have 4 elements, which must be 1, greater than 0, anything, and 5 respectively.
If you instead write:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
U
n
o
r
d
e
r
e
d
E
l
e
m
e
n
t
s
A
r
e
;
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
F
o
o
, v
o
i
d
(
c
o
n
s
t v
e
c
t
o
r

& n
u
m
b
e
r
s
)
)
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
U
n
o
r
d
e
r
e
d
E
l
e
m
e
n
t
s
A
r
e
(
1
, G
t
(
0
)
, _
, 5
)
)
)
;
It means that the container must have 4 elements, which under some permutation must be 1, greater than 0, anything, and 5 respectively.
E
l
e
m
e
n
t
s
A
r
e
(
)and U
n
o
r
d
e
r
e
d
E
l
e
m
e
n
t
s
A
r
e
(
)are overloaded to take 0 to 10 arguments. If more are needed, you can place them in a Cstyle
array and use E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
)or U
n
o
r
d
e
r
e
d
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
)instead:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
;
.
.
.
/
/ E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y a
c
c
e
p
t
s a
n a
r
r
a
y o
f e
l
e
m
e
n
t v
a
l
u
e
s
.
c
o
n
s
t i
n
t e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
1
[
] = { 1
, 5
, 2
, 4
, .
.
. }
;

c
o
n
s
t i
n
t e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
1
[
] = { 1
, 5
, 2
, 4
, .
.
. }
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
1
)
)
)
;
/
/ O
r
, a
n a
r
r
a
y o
f e
l
e
m
e
n
t m
a
t
c
h
e
r
s
.
M
a
t
c
h
e
r
 e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
2 = { 1
, G
t
(
2
)
, _
, 3
, .
.
. }
;
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
2
)
)
)
;
In case the array needs to be dynamically created (and therefore the array size cannot be inferred by the compiler), you can give
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
)an additional argument to specify the array size:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
;
.
.
.
i
n
t
* c
o
n
s
t e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
3 = n
e
w i
n
t
[
c
o
u
n
t
]
;
.
.
. f
i
l
l e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
3 w
i
t
h v
a
l
u
e
s .
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
E
l
e
m
e
n
t
s
A
r
e
A
r
r
a
y
(
e
x
p
e
c
t
e
d
_
v
e
c
t
o
r
3
, c
o
u
n
t
)
)
)
;
Tips:
E
l
e
m
e
n
t
A
r
e
*
(
)works with any container that implements the STL iterator concept (i.e. it has a c
o
n
s
t
_
i
t
e
r
a
t
o
rtype and supports
b
e
g
i
n
(
)
/
e
n
d
(
)
) and supports s
i
z
e
(
)
, not just the ones defined in STL. It will even work with container types yet to be written as long as
they follows the above pattern.
You can use nested E
l
e
m
e
n
t
A
r
e
*
(
)to match nested (multidimensional) containers.
If the container is passed by pointer instead of by reference, just write P
o
i
n
t
e
e
(
E
l
e
m
e
n
t
s
A
r
e
*
(
.
.
.
)
)
.
The order of elements matters for E
l
e
m
e
n
t
s
A
r
e
*
(
)
. Therefore don't use it with containers whose element order is undefined (e.g. h
a
s
h
_
m
a
p
).
Sharing Matchers
Under the hood, a Google Mock matcher object consists of a pointer to a refcounted implementation object. Copying matchers is allowed and
very efficient, as only the pointer is copied. When the last matcher that references the implementation object dies, the implementation object will
be deleted.
Therefore, if you have some complex matcher that you want to use again and again, there is no need to build it everytime. Just assign it to a
matcher variable and use that variable repeatedly! For example,
M
a
t
c
h
e
r
 i
n
_
r
a
n
g
e = A
l
l
O
f
(
G
t
(
5
)
, L
e
(
1
0
)
)
;
.
.
. u
s
e i
n
_
r
a
n
g
e a
s a m
a
t
c
h
e
r i
n m
u
l
t
i
p
l
e E
X
P
E
C
T
_
C
A
L
L
s .
.
.
Setting Expectations
Knowing When to Expect
O
N
_
C
A
L
Lis likely the single most underutilized construct in Google Mock.
There are basically two constructs for defining the behavior of a mock object: O
N
_
C
A
L
Land E
X
P
E
C
T
_
C
A
L
L
. The difference? O
N
_
C
A
L
Ldefines what
happens when a mock method is called, but doesn't imply any expectation on the method being called. E
X
P
E
C
T
_
C
A
L
Lnot only defines the
behavior, but also sets an expectation that the method will be called with the given arguments, for the given number of times (and in the given
order when you specify the order too).
Since E
X
P
E
C
T
_
C
A
L
Ldoes more, isn't it better than O
N
_
C
A
L
L
? Not really. Every E
X
P
E
C
T
_
C
A
L
Ladds a constraint on the behavior of the code under
test. Having more constraints than necessary is baaad even worse than not having enough constraints.
This may be counterintuitive. How could tests that verify more be worse than tests that verify less? Isn't verification the whole point of tests?
The answer, lies in what a test should verify. A good test verifies the contract of the code. If a test overspecifies, it doesn't leave enough
freedom to the implementation. As a result, changing the implementation without breaking the contract (e.g. refactoring and optimization), which
should be perfectly fine to do, can break such tests. Then you have to spend time fixing them, only to see them broken again the next time the
implementation is changed.
Keep in mind that one doesn't have to verify more than one property in one test. In fact, it's a good style to verify only one thing in one test.
If you do that, a bug will likely break only one or two tests instead of dozens (which case would you rather debug?). If you are also in the habit of
giving tests descriptive names that tell what they verify, you can often easily guess what's wrong just from the test log itself.
So use O
N
_
C
A
L
Lby default, and only use E
X
P
E
C
T
_
C
A
L
Lwhen you actually intend to verify that the call is made. For example, you may have a
bunch of O
N
_
C
A
L
L
s in your test fixture to set the common mock behavior shared by all tests in the same group, and write (scarcely) different
E
X
P
E
C
T
_
C
A
L
L
s in different T
E
S
T
_
F
s to verify different aspects of the code's behavior. Compared with the style where each T
E
S
Thas many
E
X
P
E
C
T
_
C
A
L
L
s, this leads to tests that are more resilient to implementational changes (and thus less likely to require maintenance) and makes
the intent of the tests more obvious (so they are easier to maintain when you do need to maintain them).
Ignoring Uninteresting Calls
If you are not interested in how a mock method is called, just don't say anything about it. In this case, if the method is ever called, Google Mock
will perform its default action to allow the test program to continue. If you are not happy with the default action taken by Google Mock, you can
override it using D
e
f
a
u
l
t
V
a
l
u
e
<
T
>
:
:
S
e
t
(
)(described later in this document) or O
N
_
C
A
L
L
(
)
.

override it using D
e
f
a
u
l
t
V
a
l
u
e
<
T
>
:
:
S
e
t
(
)(described later in this document) or O
N
_
C
A
L
L
(
)
.
Please note that once you expressed interest in a particular mock method (via E
X
P
E
C
T
_
C
A
L
L
(
)
), all invocations to it must match some
expectation. If this function is called but the arguments don't match any E
X
P
E
C
T
_
C
A
L
L
(
)statement, it will be an error.
Disallowing Unexpected Calls
If a mock method shouldn't be called at all, explicitly say so:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
_
)
)
.
T
i
m
e
s
(
0
)
;
If some calls to the method are allowed, but the rest are not, just list all the expected calls:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
n
y
N
u
m
b
e
r
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
t
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
5
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
G
t
(
1
0
)
)
)
.
T
i
m
e
s
(
A
n
y
N
u
m
b
e
r
(
)
)
;
A call to f
o
o
.
B
a
r
(
)that doesn't match any of the E
X
P
E
C
T
_
C
A
L
L
(
)statements will be an error.
Expecting Ordered Calls
Although an E
X
P
E
C
T
_
C
A
L
L
(
)statement defined earlier takes precedence when Google Mock tries to match a function call with an expectation,
by default calls don't have to happen in the order E
X
P
E
C
T
_
C
A
L
L
(
)statements are written. For example, if the arguments match the matchers in
the third E
X
P
E
C
T
_
C
A
L
L
(
)
, but not those in the first two, then the third expectation will be used.
If you would rather have all calls occur in the order of the expectations, put the E
X
P
E
C
T
_
C
A
L
L
(
)statements in a block where you define a
variable of type I
n
S
e
q
u
e
n
c
e
:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
S
e
q
u
e
n
c
e
;
{
I
n
S
e
q
u
e
n
c
e s
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
5
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
b
a
r
, D
o
T
h
a
t
(
_
)
)
.
T
i
m
e
s
(
2
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
6
)
)
;
}
In this example, we expect a call to f
o
o
.
D
o
T
h
i
s
(
5
)
, followed by two calls to b
a
r
.
D
o
T
h
a
t
(
)where the argument can be anything, which are in
turn followed by a call to f
o
o
.
D
o
T
h
i
s
(
6
)
. If a call occurred outoforder, Google Mock will report an error.
Expecting Partially Ordered Calls
Sometimes requiring everything to occur in a predetermined order can lead to brittle tests. For example, we may care about Aoccurring before
both Band C
, but aren't interested in the relative order of Band C
. In this case, the test should reflect our real intent, instead of being overly
constraining.
Google Mock allows you to impose an arbitrary DAG (directed acyclic graph) on the calls. One way to express the DAG is to use the After
clause of E
X
P
E
C
T
_
C
A
L
L
.
Another way is via the I
n
S
e
q
u
e
n
c
e
(
)clause (not the same as the I
n
S
e
q
u
e
n
c
eclass), which we borrowed from jMock 2. It's less flexible than
A
f
t
e
r
(
)
, but more convenient when you have long chains of sequential calls, as it doesn't require you to come up with different names for the
expectations in the chains. Here's how it works:
If we view E
X
P
E
C
T
_
C
A
L
L
(
)statements as nodes in a graph, and add an edge from node A to node B wherever A must occur before B, we can
get a DAG. We use the term "sequence" to mean a directed path in this DAG. Now, if we decompose the DAG into sequences, we just need to
know which sequences each E
X
P
E
C
T
_
C
A
L
L
(
)belongs to in order to be able to reconstruct the orginal DAG.
So, to specify the partial order on the expectations we need to do two things: first to define some S
e
q
u
e
n
c
eobjects, and then for each
E
X
P
E
C
T
_
C
A
L
L
(
)say which S
e
q
u
e
n
c
eobjects it is part of. Expectations in the same sequence must occur in the order they are written. For
example,
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
q
u
e
n
c
e
;
S
e
q
u
e
n
c
e s
1
, s
2
;

S
e
q
u
e
n
c
e s
1
, s
2
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, A
(
)
)
.
I
n
S
e
q
u
e
n
c
e
(
s
1
, s
2
)
;
E
X
P
E
C
T
_
C
A
L
L
(
b
a
r
, B
(
)
)
.
I
n
S
e
q
u
e
n
c
e
(
s
1
)
;
E
X
P
E
C
T
_
C
A
L
L
(
b
a
r
, C
(
)
)
.
I
n
S
e
q
u
e
n
c
e
(
s
2
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
(
)
)
.
I
n
S
e
q
u
e
n
c
e
(
s
2
)
;
specifies the following DAG (where s
1is A -
> B
, and s
2is `A > C > D`):
+
-
-
-
> B
|
A -
-
-
|
|
+
-
-
-
> C -
-
-
> D
This means that A must occur before B and C, and C must occur before D. There's no restriction about the order other than these.
Controlling When an Expectation Retires
When a mock method is called, Google Mock only consider expectations that are still active. An expectation is active when created, and
becomes inactive (aka retires) when a call that has to occur later has occurred. For example, in
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
q
u
e
n
c
e
;
S
e
q
u
e
n
c
e s
1
, s
2
;
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, "
F
i
l
e t
o
o l
a
r
g
e
.
"
)
) /
/ #
1
.
T
i
m
e
s
(
A
n
y
N
u
m
b
e
r
(
)
)
.
I
n
S
e
q
u
e
n
c
e
(
s
1
, s
2
)
;
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, "
D
a
t
a s
e
t i
s e
m
p
t
y
.
"
)
) /
/ #
2
.
I
n
S
e
q
u
e
n
c
e
(
s
1
)
;
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, "
U
s
e
r n
o
t f
o
u
n
d
.
"
)
) /
/ #
3
.
I
n
S
e
q
u
e
n
c
e
(
s
2
)
;
as soon as either #2 or #3 is matched, #1 will retire. If a warning "
F
i
l
e t
o
o l
a
r
g
e
.
"is logged after this, it will be an error.
Note that an expectation doesn't retire automatically when it's saturated. For example,
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, _
)
)
; /
/ #
1
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, "
F
i
l
e t
o
o l
a
r
g
e
.
"
)
)
; /
/ #
2
says that there will be exactly one warning with the message `"File too large."`. If the second warning contains this message too, #2 will match
again and result in an upperboundviolated error.
If this is not what you want, you can ask an expectation to retire as soon as it becomes saturated:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, _
)
)
; /
/ #
1
E
X
P
E
C
T
_
C
A
L
L
(
l
o
g
, L
o
g
(
W
A
R
N
I
N
G
, _
, "
F
i
l
e t
o
o l
a
r
g
e
.
"
)
) /
/ #
2
.
R
e
t
i
r
e
s
O
n
S
a
t
u
r
a
t
i
o
n
(
)
;
Here #2 can be used only once, so if you have two warnings with the message "
F
i
l
e t
o
o l
a
r
g
e
.
"
, the first will match #2 and the second will
match #1 there will be no error.
Using Actions
Returning References from Mock Methods
If a mock function's return type is a reference, you need to use R
e
t
u
r
n
R
e
f
(
)instead of R
e
t
u
r
n
(
)to return a result:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
R
e
f
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {

c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
0
(
G
e
t
B
a
r
, B
a
r
&
(
)
)
;
}
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
B
a
r b
a
r
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, G
e
t
B
a
r
(
)
)
.
W
i
l
l
O
n
c
e
(
R
e
t
u
r
n
R
e
f
(
b
a
r
)
)
;
Returning Live Values from Mock Methods
The R
e
t
u
r
n
(
x
)action saves a copy of xwhen the action is created, and always returns the same value whenever it's executed. Sometimes you
may want to instead return the live value of x(i.e. its value at the time when the action is executed.).
If the mock function's return type is a reference, you can do it using R
e
t
u
r
n
R
e
f
(
x
)
, as shown in the previous recipe ("Returning References from
Mock Methods"). However, Google Mock doesn't let you use R
e
t
u
r
n
R
e
f
(
)in a mock function whose return type is not a reference, as doing that
usually indicates a user error. So, what shall you do?
You may be tempted to try B
y
R
e
f
(
)
:
u
s
i
n
g t
e
s
t
i
n
g
:
:
B
y
R
e
f
;
u
s
i
n
g t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
0
(
G
e
t
V
a
l
u
e
, i
n
t
(
)
)
;
}
;
.
.
.
i
n
t x = 0
;
M
o
c
k
F
o
o f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, G
e
t
V
a
l
u
e
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
(
B
y
R
e
f
(
x
)
)
)
;
x = 4
2
;
E
X
P
E
C
T
_
E
Q
(
4
2
, f
o
o
.
G
e
t
V
a
l
u
e
(
)
)
;
Unfortunately, it doesn't work here. The above code will fail with error:
V
a
l
u
e o
f
: f
o
o
.
G
e
t
V
a
l
u
e
(
)
A
c
t
u
a
l
: 0
E
x
p
e
c
t
e
d
: 4
2
The reason is that R
e
t
u
r
n
(
v
a
l
u
e
)converts v
a
l
u
eto the actual return type of the mock function at the time when the action is created, not
when it is executed. (This behavior was chosen for the action to be safe when v
a
l
u
eis a proxy object that references some temporary objects.)
As a result, B
y
R
e
f
(
x
)is converted to an i
n
tvalue (instead of a c
o
n
s
t i
n
t
&
) when the expectation is set, and R
e
t
u
r
n
(
B
y
R
e
f
(
x
)
)will always
return 0.
R
e
t
u
r
n
P
o
i
n
t
e
e
(
p
o
i
n
t
e
r
)was provided to solve this problem specifically. It returns the value pointed to by p
o
i
n
t
e
rat the time the action is
executed:
u
s
i
n
g t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
P
o
i
n
t
e
e
;
.
.
.
i
n
t x = 0
;
M
o
c
k
F
o
o f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, G
e
t
V
a
l
u
e
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
P
o
i
n
t
e
e
(
&
x
)
)
; /
/ N
o
t
e t
h
e & h
e
r
e
.
x = 4
2
;
E
X
P
E
C
T
_
E
Q
(
4
2
, f
o
o
.
G
e
t
V
a
l
u
e
(
)
)
; /
/ T
h
i
s w
i
l
l s
u
c
c
e
e
d n
o
w
.
Combining Actions
Want to do more than one thing when a function is called? That's fine. D
o
A
l
l
(
)allow you to do sequence of actions every time. Only the return
value of the last action in the sequence will be used.
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
D
o
A
l
l
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
B
a
r
, b
o
o
l
(
i
n
t n
)
)
;
}
;
.
.
.

.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
_
)
)
.
W
i
l
l
O
n
c
e
(
D
o
A
l
l
(
a
c
t
i
o
n
_
1
,
a
c
t
i
o
n
_
2
,
.
.
.
a
c
t
i
o
n
_
n
)
)
;
Mocking Side Effects
Sometimes a method exhibits its effect not via returning a value but via side effects. For example, it may change some global state or modify an
output argument. To mock side effects, in general you can define your own action by implementing :
:
t
e
s
t
i
n
g
:
:
A
c
t
i
o
n
I
n
t
e
r
f
a
c
e
.
If all you need to do is to change an output argument, the builtin S
e
t
A
r
g
P
o
i
n
t
e
e
(
)action is convenient:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
t
A
r
g
P
o
i
n
t
e
e
;
c
l
a
s
s M
o
c
k
M
u
t
a
t
o
r : p
u
b
l
i
c M
u
t
a
t
o
r {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
2
(
M
u
t
a
t
e
, v
o
i
d
(
b
o
o
l m
u
t
a
t
e
, i
n
t
* v
a
l
u
e
)
)
;
.
.
.
}
;
.
.
.
M
o
c
k
M
u
t
a
t
o
r m
u
t
a
t
o
r
;
E
X
P
E
C
T
_
C
A
L
L
(
m
u
t
a
t
o
r
, M
u
t
a
t
e
(
t
r
u
e
, _
)
)
.
W
i
l
l
O
n
c
e
(
S
e
t
A
r
g
P
o
i
n
t
e
e
<
1
>
(
5
)
)
;
In this example, when m
u
t
a
t
o
r
.
M
u
t
a
t
e
(
)is called, we will assign 5 to the i
n
tvariable pointed to by argument #1 (0based).
S
e
t
A
r
g
P
o
i
n
t
e
e
(
)conveniently makes an internal copy of the value you pass to it, removing the need to keep the value in scope and alive. The
implication however is that the value must have a copy constructor and assignment operator.
If the mock method also needs to return a value as well, you can chain S
e
t
A
r
g
P
o
i
n
t
e
e
(
)with R
e
t
u
r
n
(
)using D
o
A
l
l
(
)
:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
t
A
r
g
P
o
i
n
t
e
e
;
c
l
a
s
s M
o
c
k
M
u
t
a
t
o
r : p
u
b
l
i
c M
u
t
a
t
o
r {
p
u
b
l
i
c
:
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
M
u
t
a
t
e
I
n
t
, b
o
o
l
(
i
n
t
* v
a
l
u
e
)
)
;
}
;
.
.
.
M
o
c
k
M
u
t
a
t
o
r m
u
t
a
t
o
r
;
E
X
P
E
C
T
_
C
A
L
L
(
m
u
t
a
t
o
r
, M
u
t
a
t
e
I
n
t
(
_
)
)
.
W
i
l
l
O
n
c
e
(
D
o
A
l
l
(
S
e
t
A
r
g
P
o
i
n
t
e
e
<
0
>
(
5
)
,
R
e
t
u
r
n
(
t
r
u
e
)
)
)
;
If the output argument is an array, use the S
e
t
A
r
r
a
y
A
r
g
u
m
e
n
t
<
N
>
(
f
i
r
s
t
, l
a
s
t
)action instead. It copies the elements in source range
[
f
i
r
s
t
, l
a
s
t
)to the array pointed to by the N
th (0based) argument:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
N
o
t
N
u
l
l
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
t
A
r
r
a
y
A
r
g
u
m
e
n
t
;
c
l
a
s
s M
o
c
k
A
r
r
a
y
M
u
t
a
t
o
r : p
u
b
l
i
c A
r
r
a
y
M
u
t
a
t
o
r {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
2
(
M
u
t
a
t
e
, v
o
i
d
(
i
n
t
* v
a
l
u
e
s
, i
n
t n
u
m
_
v
a
l
u
e
s
)
)
;
.
.
.
}
;
.
.
.
M
o
c
k
A
r
r
a
y
M
u
t
a
t
o
r m
u
t
a
t
o
r
;
i
n
t v
a
l
u
e
s
[
5
] = { 1
, 2
, 3
, 4
, 5 }
;
E
X
P
E
C
T
_
C
A
L
L
(
m
u
t
a
t
o
r
, M
u
t
a
t
e
(
N
o
t
N
u
l
l
(
)
, 5
)
)
.
W
i
l
l
O
n
c
e
(
S
e
t
A
r
r
a
y
A
r
g
u
m
e
n
t
<
0
>
(
v
a
l
u
e
s
, v
a
l
u
e
s + 5
)
)
;
This also works when the argument is an output iterator:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;

u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
e
A
r
r
a
y
A
r
g
u
m
e
n
t
;
c
l
a
s
s M
o
c
k
R
o
l
o
d
e
x : p
u
b
l
i
c R
o
l
o
d
e
x {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
G
e
t
N
a
m
e
s
, v
o
i
d
(
s
t
d
:
:
b
a
c
k
_
i
n
s
e
r
t
_
i
t
e
r
a
t
o
r
<
v
e
c
t
o
r
<
s
t
r
i
n
g
> >
)
)
;
.
.
.
}
;
.
.
.
M
o
c
k
R
o
l
o
d
e
x r
o
l
o
d
e
x
;
v
e
c
t
o
r
<
s
t
r
i
n
g
> n
a
m
e
s
;
n
a
m
e
s
.
p
u
s
h
_
b
a
c
k
(
"
G
e
o
r
g
e
"
)
;
n
a
m
e
s
.
p
u
s
h
_
b
a
c
k
(
"
J
o
h
n
"
)
;
n
a
m
e
s
.
p
u
s
h
_
b
a
c
k
(
"
T
h
o
m
a
s
"
)
;
E
X
P
E
C
T
_
C
A
L
L
(
r
o
l
o
d
e
x
, G
e
t
N
a
m
e
s
(
_
)
)
.
W
i
l
l
O
n
c
e
(
S
e
t
A
r
r
a
y
A
r
g
u
m
e
n
t
<
0
>
(
n
a
m
e
s
.
b
e
g
i
n
(
)
, n
a
m
e
s
.
e
n
d
(
)
)
)
;
Changing a Mock Object's Behavior Based on the State
If you expect a call to change the behavior of a mock object, you can use :
:
t
e
s
t
i
n
g
:
:
I
n
S
e
q
u
e
n
c
eto specify different behaviors before and
after the call:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
S
e
q
u
e
n
c
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
.
.
.
{
I
n
S
e
q
u
e
n
c
e s
e
q
;
E
X
P
E
C
T
_
C
A
L
L
(
m
y
_
m
o
c
k
, I
s
D
i
r
t
y
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
(
t
r
u
e
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
m
y
_
m
o
c
k
, F
l
u
s
h
(
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
m
y
_
m
o
c
k
, I
s
D
i
r
t
y
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
(
f
a
l
s
e
)
)
;
}
m
y
_
m
o
c
k
.
F
l
u
s
h
I
f
D
i
r
t
y
(
)
;
This makes m
y
_
m
o
c
k
.
I
s
D
i
r
t
y
(
)return t
r
u
ebefore m
y
_
m
o
c
k
.
F
l
u
s
h
(
)is called and return f
a
l
s
eafterwards.
If the behavior change is more complex, you can store the effects in a variable and make a mock method get its return value from that variable:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
S
a
v
e
A
r
g
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
A
C
T
I
O
N
_
P
(
R
e
t
u
r
n
P
o
i
n
t
e
e
, p
) { r
e
t
u
r
n *
p
; }
.
.
.
i
n
t p
r
e
v
i
o
u
s
_
v
a
l
u
e = 0
;
E
X
P
E
C
T
_
C
A
L
L
(
m
y
_
m
o
c
k
, G
e
t
P
r
e
v
V
a
l
u
e
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
R
e
t
u
r
n
P
o
i
n
t
e
e
(
&
p
r
e
v
i
o
u
s
_
v
a
l
u
e
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
m
y
_
m
o
c
k
, U
p
d
a
t
e
V
a
l
u
e
(
_
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
S
a
v
e
A
r
g
<
0
>
(
&
p
r
e
v
i
o
u
s
_
v
a
l
u
e
)
)
;
m
y
_
m
o
c
k
.
D
o
S
o
m
e
t
h
i
n
g
T
o
U
p
d
a
t
e
V
a
l
u
e
(
)
;
Here m
y
_
m
o
c
k
.
G
e
t
P
r
e
v
V
a
l
u
e
(
)will always return the argument of the last U
p
d
a
t
e
V
a
l
u
e
(
)call.
Setting the Default Value for a Return Type
If a mock method's return type is a builtin C++ type or pointer, by default it will return 0 when invoked. You only need to specify an action if this
default value doesn't work for you.
Sometimes, you may want to change this default value, or you may want to specify a default value for types Google Mock doesn't know about.
You can do this using the :
:
t
e
s
t
i
n
g
:
:
D
e
f
a
u
l
t
V
a
l
u
eclass template:
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
0
(
C
a
l
c
u
l
a
t
e
B
a
r
, B
a
r
(
)
)
;
}
;
.
.
.
B
a
r d
e
f
a
u
l
t
_
b
a
r
;
/
/ S
e
t
s t
h
e d
e
f
a
u
l
t r
e
t
u
r
n v
a
l
u
e f
o
r t
y
p
e B
a
r
.

/
/ S
e
t
s t
h
e d
e
f
a
u
l
t r
e
t
u
r
n v
a
l
u
e f
o
r t
y
p
e B
a
r
.
D
e
f
a
u
l
t
V
a
l
u
e

:
:
S
e
t
(
d
e
f
a
u
l
t
_
b
a
r
)
;
M
o
c
k
F
o
o f
o
o
;
/
/ W
e d
o
n
'
t n
e
e
d t
o s
p
e
c
i
f
y a
n a
c
t
i
o
n h
e
r
e
, a
s t
h
e d
e
f
a
u
l
t
/
/ r
e
t
u
r
n v
a
l
u
e w
o
r
k
s f
o
r u
s
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, C
a
l
c
u
l
a
t
e
B
a
r
(
)
)
;
f
o
o
.
C
a
l
c
u
l
a
t
e
B
a
r
(
)
; /
/ T
h
i
s s
h
o
u
l
d r
e
t
u
r
n d
e
f
a
u
l
t
_
b
a
r
.
/
/ U
n
s
e
t
s t
h
e d
e
f
a
u
l
t r
e
t
u
r
n v
a
l
u
e
.
D
e
f
a
u
l
t
V
a
l
u
e

:
:
C
l
e
a
r
(
)
;
Please note that changing the default value for a type can make you tests hard to understand. We recommend you to use this feature
judiciously. For example, you may want to make sure the S
e
t
(
)and C
l
e
a
r
(
)calls are right next to the code that uses your mock.
Setting the Default Actions for a Mock Method
You've learned how to change the default value of a given type. However, this may be too coarse for your purpose: perhaps you have two mock
methods with the same return type and you want them to have different behaviors. The O
N
_
C
A
L
L
(
)macro allows you to customize your mock's
behavior at the method level:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
A
n
y
N
u
m
b
e
r
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
G
t
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
.
.
.
O
N
_
C
A
L
L
(
f
o
o
, S
i
g
n
(
_
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
R
e
t
u
r
n
(
-
1
)
)
;
O
N
_
C
A
L
L
(
f
o
o
, S
i
g
n
(
0
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
R
e
t
u
r
n
(
0
)
)
;
O
N
_
C
A
L
L
(
f
o
o
, S
i
g
n
(
G
t
(
0
)
)
)
.
W
i
l
l
B
y
D
e
f
a
u
l
t
(
R
e
t
u
r
n
(
1
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, S
i
g
n
(
_
)
)
.
T
i
m
e
s
(
A
n
y
N
u
m
b
e
r
(
)
)
;
f
o
o
.
S
i
g
n
(
5
)
; /
/ T
h
i
s s
h
o
u
l
d r
e
t
u
r
n 1
.
f
o
o
.
S
i
g
n
(
-
9
)
; /
/ T
h
i
s s
h
o
u
l
d r
e
t
u
r
n -
1
.
f
o
o
.
S
i
g
n
(
0
)
; /
/ T
h
i
s s
h
o
u
l
d r
e
t
u
r
n 0
.
As you may have guessed, when there are more than one O
N
_
C
A
L
L
(
)statements, the news order take precedence over the older ones. In other
words, the last one that matches the function arguments will be used. This matching order allows you to set up the common behavior in a mock
object's constructor or the test fixture's setup phase and specialize the mock's behavior later.
Using Functions/Methods/Functors as Actions
If the builtin actions don't suit you, you can easily use an existing function, method, or functor as an action:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
2
(
S
u
m
, i
n
t
(
i
n
t x
, i
n
t y
)
)
;
M
O
C
K
_
M
E
T
H
O
D
1
(
C
o
m
p
l
e
x
J
o
b
, b
o
o
l
(
i
n
t x
)
)
;
}
;
i
n
t C
a
l
c
u
l
a
t
e
S
u
m
(
i
n
t x
, i
n
t y
) { r
e
t
u
r
n x + y
; }
c
l
a
s
s H
e
l
p
e
r {
p
u
b
l
i
c
:
b
o
o
l C
o
m
p
l
e
x
J
o
b
(
i
n
t x
)
;
}
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
H
e
l
p
e
r h
e
l
p
e
r
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, S
u
m
(
_
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
C
a
l
c
u
l
a
t
e
S
u
m
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, C
o
m
p
l
e
x
J
o
b
(
_
)
)

E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, C
o
m
p
l
e
x
J
o
b
(
_
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
&
h
e
l
p
e
r
, &
H
e
l
p
e
r
:
:
C
o
m
p
l
e
x
J
o
b
)
)
;
f
o
o
.
S
u
m
(
5
, 6
)
; /
/ I
n
v
o
k
e
s C
a
l
c
u
l
a
t
e
S
u
m
(
5
, 6
)
.
f
o
o
.
C
o
m
p
l
e
x
J
o
b
(
1
0
)
; /
/ I
n
v
o
k
e
s h
e
l
p
e
r
.
C
o
m
p
l
e
x
J
o
b
(
1
0
)
;
The only requirement is that the type of the function, etc must be compatible with the signature of the mock function, meaning that the latter's
arguments can be implicitly converted to the corresponding arguments of the former, and the former's return type can be implicitly converted to
that of the latter. So, you can invoke something whose type is not exactly the same as the mock function, as long as it's safe to do so nice,
huh?
Invoking a Function/Method/Functor Without Arguments
I
n
v
o
k
e
(
)is very useful for doing actions that are more complex. It passes the mock function's arguments to the function or functor being
invoked such that the callee has the full context of the call to work with. If the invoked function is not interested in some or all of the arguments,
it can simply ignore them.
Yet, a common pattern is that a test author wants to invoke a function without the arguments of the mock function. I
n
v
o
k
e
(
)allows her to do
that using a wrapper function that throws away the arguments before invoking an underlining nullary function. Needless to say, this can be
tedious and obscures the intent of the test.
I
n
v
o
k
e
W
i
t
h
o
u
t
A
r
g
s
(
)solves this problem. It's like I
n
v
o
k
e
(
)except that it doesn't pass the mock function's arguments to the callee. Here's an
example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
W
i
t
h
o
u
t
A
r
g
s
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
C
o
m
p
l
e
x
J
o
b
, b
o
o
l
(
i
n
t n
)
)
;
}
;
b
o
o
l J
o
b
1
(
) { .
.
. }
.
.
.
M
o
c
k
F
o
o f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, C
o
m
p
l
e
x
J
o
b
(
_
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
W
i
t
h
o
u
t
A
r
g
s
(
J
o
b
1
)
)
;
f
o
o
.
C
o
m
p
l
e
x
J
o
b
(
1
0
)
; /
/ I
n
v
o
k
e
s J
o
b
1
(
)
.
Invoking an Argument of the Mock Function
Sometimes a mock function will receive a function pointer or a functor (in other words, a "callable") as an argument, e.g.
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
2
(
D
o
T
h
i
s
, b
o
o
l
(
i
n
t n
, b
o
o
l (
*
f
p
)
(
i
n
t
)
)
)
;
}
;
and you may want to invoke this callable argument:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
_
, _
)
)
.
W
i
l
l
O
n
c
e
(
.
.
.
)
;
/
/ W
i
l
l e
x
e
c
u
t
e (
*
f
p
)
(
5
)
, w
h
e
r
e f
p i
s t
h
e
/
/ s
e
c
o
n
d a
r
g
u
m
e
n
t D
o
T
h
i
s
(
) r
e
c
e
i
v
e
s
.
Arghh, you need to refer to a mock function argument but C++ has no lambda (yet), so you have to define your own action. :( Or do you really?
Well, Google Mock has an action to solve exactly this problem:
I
n
v
o
k
e
A
r
g
u
m
e
n
t
<
N
>
(
a
r
g
_
1
, a
r
g
_
2
, .
.
.
, a
r
g
_
m
)
will invoke the N
th (0based) argument the mock function receives, with a
r
g
_
1
, a
r
g
_
2
, ..., and a
r
g
_
m
. No matter if the argument is a function
pointer or a functor, Google Mock handles them both.
With that, you could write:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
A
r
g
u
m
e
n
t
;

u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
A
r
g
u
m
e
n
t
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
_
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
A
r
g
u
m
e
n
t
<
1
>
(
5
)
)
;
/
/ W
i
l
l e
x
e
c
u
t
e (
*
f
p
)
(
5
)
, w
h
e
r
e f
p i
s t
h
e
/
/ s
e
c
o
n
d a
r
g
u
m
e
n
t D
o
T
h
i
s
(
) r
e
c
e
i
v
e
s
.
What if the callable takes an argument by reference? No problem just wrap it inside B
y
R
e
f
(
)
:
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
B
a
r
, b
o
o
l
(
b
o
o
l (
*
f
p
)
(
i
n
t
, c
o
n
s
t H
e
l
p
e
r
&
)
)
)
;
.
.
.
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
B
y
R
e
f
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
A
r
g
u
m
e
n
t
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
H
e
l
p
e
r h
e
l
p
e
r
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, B
a
r
(
_
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
A
r
g
u
m
e
n
t
<
0
>
(
5
, B
y
R
e
f
(
h
e
l
p
e
r
)
)
)
;
/
/ B
y
R
e
f
(
h
e
l
p
e
r
) g
u
a
r
a
n
t
e
e
s t
h
a
t a r
e
f
e
r
e
n
c
e t
o h
e
l
p
e
r
, n
o
t a c
o
p
y o
f i
t
,
/
/ w
i
l
l b
e p
a
s
s
e
d t
o t
h
e c
a
l
l
a
b
l
e
.
What if the callable takes an argument by reference and we do not wrap the argument in B
y
R
e
f
(
)
? Then I
n
v
o
k
e
A
r
g
u
m
e
n
t
(
)will make a copy of
the argument, and pass a reference to the copy, instead of a reference to the original value, to the callable. This is especially handy when the
argument is a temporary value:
.
.
.
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
a
t
, b
o
o
l
(
b
o
o
l (
*
f
)
(
c
o
n
s
t d
o
u
b
l
e
& x
, c
o
n
s
t s
t
r
i
n
g
& s
)
)
)
;
.
.
.
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
A
r
g
u
m
e
n
t
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
_
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
A
r
g
u
m
e
n
t
<
0
>
(
5
.
0
, s
t
r
i
n
g
(
"
H
i
"
)
)
)
;
/
/ W
i
l
l e
x
e
c
u
t
e (
*
f
)
(
5
.
0
, s
t
r
i
n
g
(
"
H
i
"
)
)
, w
h
e
r
e f i
s t
h
e f
u
n
c
t
i
o
n p
o
i
n
t
e
r
/
/ D
o
T
h
a
t
(
) r
e
c
e
i
v
e
s
. N
o
t
e t
h
a
t t
h
e v
a
l
u
e
s 5
.
0 a
n
d s
t
r
i
n
g
(
"
H
i
"
) a
r
e
/
/ t
e
m
p
o
r
a
r
y a
n
d d
e
a
d o
n
c
e t
h
e E
X
P
E
C
T
_
C
A
L
L
(
) s
t
a
t
e
m
e
n
t f
i
n
i
s
h
e
s
. Y
e
t
/
/ i
t
'
s f
i
n
e t
o p
e
r
f
o
r
m t
h
i
s a
c
t
i
o
n l
a
t
e
r
, s
i
n
c
e a c
o
p
y o
f t
h
e v
a
l
u
e
s
/
/ a
r
e k
e
p
t i
n
s
i
d
e t
h
e I
n
v
o
k
e
A
r
g
u
m
e
n
t a
c
t
i
o
n
.
Ignoring an Action's Result
Sometimes you have an action that returns something, but you need an action that returns v
o
i
d(perhaps you want to use it in a mock function
that returns v
o
i
d
, or perhaps it needs to be used in D
o
A
l
l
(
)and it's not the last in the list). I
g
n
o
r
e
R
e
s
u
l
t
(
)lets you do that. For example:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
R
e
t
u
r
n
;
i
n
t P
r
o
c
e
s
s
(
c
o
n
s
t M
y
D
a
t
a
& d
a
t
a
)
;
s
t
r
i
n
g D
o
S
o
m
e
t
h
i
n
g
(
)
;
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
M
O
C
K
_
M
E
T
H
O
D
1
(
A
b
c
, v
o
i
d
(
c
o
n
s
t M
y
D
a
t
a
& d
a
t
a
)
)
;
M
O
C
K
_
M
E
T
H
O
D
0
(
X
y
z
, b
o
o
l
(
)
)
;
}
;
.
.
.
M
o
c
k
F
o
o f
o
o
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, A
b
c
(
_
)
)
/
/ .
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
P
r
o
c
e
s
s
)
)
;
/
/ T
h
e a
b
o
v
e l
i
n
e w
o
n
'
t c
o
m
p
i
l
e a
s P
r
o
c
e
s
s
(
) r
e
t
u
r
n
s i
n
t b
u
t A
b
c
(
) n
e
e
d
s
/
/ t
o r
e
t
u
r
n v
o
i
d
.
.
W
i
l
l
O
n
c
e
(
I
g
n
o
r
e
R
e
s
u
l
t
(
I
n
v
o
k
e
(
P
r
o
c
e
s
s
)
)
)
;

.
W
i
l
l
O
n
c
e
(
I
g
n
o
r
e
R
e
s
u
l
t
(
I
n
v
o
k
e
(
P
r
o
c
e
s
s
)
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, X
y
z
(
)
)
.
W
i
l
l
O
n
c
e
(
D
o
A
l
l
(
I
g
n
o
r
e
R
e
s
u
l
t
(
I
n
v
o
k
e
(
D
o
S
o
m
e
t
h
i
n
g
)
)
,
/
/ I
g
n
o
r
e
s t
h
e s
t
r
i
n
g D
o
S
o
m
e
t
h
i
n
g
(
) r
e
t
u
r
n
s
.
R
e
t
u
r
n
(
t
r
u
e
)
)
)
;
Note that you cannot use I
g
n
o
r
e
R
e
s
u
l
t
(
)on an action that already returns v
o
i
d
. Doing so will lead to ugly compiler errors.
Say you have a mock function F
o
o
(
)that takes seven arguments, and you have a custom action that you want to invoke when F
o
o
(
)is called.
Trouble is, the custom action only wants three arguments:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
.
.
.
M
O
C
K
_
M
E
T
H
O
D
7
(
F
o
o
, b
o
o
l
(
b
o
o
l v
i
s
i
b
l
e
, c
o
n
s
t s
t
r
i
n
g
& n
a
m
e
, i
n
t x
, i
n
t y
,
c
o
n
s
t m
a
p

, d
o
u
b
l
e
>
& w
e
i
g
h
t
,
d
o
u
b
l
e m
i
n
_
w
e
i
g
h
t
, d
o
u
b
l
e m
a
x
_
w
i
g
h
t
)
)
;
.
.
.
b
o
o
l I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
(
b
o
o
l v
i
s
i
b
l
e
, i
n
t x
, i
n
t y
) {
r
e
t
u
r
n v
i
s
i
b
l
e &
& x >
= 0 &
& y >
= 0
;
}
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
_
, _
, _
, _
, _
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
)
)
; /
/ U
h
, w
o
n
'
t c
o
m
p
i
l
e
. :
-
(
To please the compiler God, you can to define an "adaptor" that has the same signature as F
o
o
(
)and calls the custom action with the right
arguments:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
b
o
o
l M
y
I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
(
b
o
o
l v
i
s
i
b
l
e
, c
o
n
s
t s
t
r
i
n
g
& n
a
m
e
, i
n
t x
, i
n
t y
,
c
o
n
s
t m
a
p

, d
o
u
b
l
e
>
& w
e
i
g
h
t
,
d
o
u
b
l
e m
i
n
_
w
e
i
g
h
t
, d
o
u
b
l
e m
a
x
_
w
i
g
h
t
) {
r
e
t
u
r
n I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
(
v
i
s
i
b
l
e
, x
, y
)
;
}
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
_
, _
, _
, _
, _
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
M
y
I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
)
)
; /
/ N
o
w i
t w
o
r
k
s
.
But isn't this awkward?
Google Mock provides a generic action adaptor, so you can spend your time minding more important business than writing your own adaptors.
Here's the syntax:
W
i
t
h
A
r
g
s
<
N
1
, N
2
, .
.
.
, N
k
>
(
a
c
t
i
o
n
)
creates an action that passes the arguments of the mock function at the given indices (0based) to the inner a
c
t
i
o
nand performs it. Using
W
i
t
h
A
r
g
s
, our original example can be written as:
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
W
i
t
h
A
r
g
s
;
.
.
.
E
X
P
E
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
_
, _
, _
, _
, _
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
W
i
t
h
A
r
g
s
<
0
, 2
, 3
>
(
I
n
v
o
k
e
(
I
s
V
i
s
i
b
l
e
I
n
Q
u
a
d
r
a
n
t
1
)
)
)
;
/
/ N
o n
e
e
d t
o d
e
f
i
n
e y
o
u
r o
w
n a
d
a
p
t
o
r
.
For better readability, Google Mock also gives you:
W
i
t
h
o
u
t
A
r
g
s
(
a
c
t
i
o
n
)when the inner a
c
t
i
o
ntakes no argument, and
W
i
t
h
A
r
g
<
N
>
(
a
c
t
i
o
n
)(no safter A
r
g
) when the inner a
c
t
i
o
ntakes one argument.
As you may have realized, I
n
v
o
k
e
W
i
t
h
o
u
t
A
r
g
s
(
.
.
.
)is just syntactic sugar for W
i
t
h
o
u
t
A
r
g
s
(
I
n
o
v
k
e
(
.
.
.
)
)
.
Here are more tips:

Here are more tips:
The inner action used in W
i
t
h
A
r
g
sand friends does not have to be I
n
v
o
k
e
(
) it can be anything.
You can repeat an argument in the argument list if necessary, e.g. W
i
t
h
A
r
g
s
<
2
, 3
, 3
, 5
>
(
.
.
.
)
.
You can change the order of the arguments, e.g. W
i
t
h
A
r
g
s
<
3
, 2
, 1
>
(
.
.
.
)
.
The types of the selected arguments do not have to match the signature of the inner action exactly. It works as long as they can be
implicitly converted to the corresponding arguments of the inner action. For example, if the 4th argument of the mock function is an i
n
tand
m
y
_
a
c
t
i
o
ntakes a d
o
u
b
l
e
, W
i
t
h
A
r
g
<
4
>
(
m
y
_
a
c
t
i
o
n
)will work.
Ignoring Arguments in Action Functions
The selectinganaction'sarguments recipe showed us one way to make a mock function and an action with incompatible argument lists fit
together. The downside is that wrapping the action in W
i
t
h
A
r
g
s
<
.
.
.
>
(
)can get tedious for people writing the tests.
If you are defining a function, method, or functor to be used with I
n
v
o
k
e
*
(
)
, and you are not interested in some of its arguments, an alternative
to W
i
t
h
A
r
g
sis to declare the uninteresting arguments as U
n
u
s
e
d
. This makes the definition less cluttered and less fragile in case the types of
the uninteresting arguments change. It could also increase the chance the action function can be reused. For example, given
M
O
C
K
_
M
E
T
H
O
D
3
(
F
o
o
, d
o
u
b
l
e
(
c
o
n
s
t s
t
r
i
n
g
& l
a
b
e
l
, d
o
u
b
l
e x
, d
o
u
b
l
e y
)
)
;
M
O
C
K
_
M
E
T
H
O
D
3
(
B
a
r
, d
o
u
b
l
e
(
i
n
t i
n
d
e
x
, d
o
u
b
l
e x
, d
o
u
b
l
e y
)
)
;
instead of
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
d
o
u
b
l
e D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
W
i
t
h
L
a
b
e
l
(
c
o
n
s
t s
t
r
i
n
g
& l
a
b
e
l
, d
o
u
b
l
e x
, d
o
u
b
l
e y
) {
r
e
t
u
r
n s
q
r
t
(
x
*
x + y
*
y
)
;
}
d
o
u
b
l
e D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
W
i
t
h
I
n
d
e
x
(
i
n
t i
n
d
e
x
, d
o
u
b
l
e x
, d
o
u
b
l
e y
) {
r
e
t
u
r
n s
q
r
t
(
x
*
x + y
*
y
)
;
}
.
.
.
E
X
E
P
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
"
a
b
c
"
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
W
i
t
h
L
a
b
e
l
)
)
;
E
X
E
P
C
T
_
C
A
L
L
(
m
o
c
k
, B
a
r
(
5
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
W
i
t
h
I
n
d
e
x
)
)
;
you could write
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
_
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
I
n
v
o
k
e
;
u
s
i
n
g :
:
t
e
s
t
i
n
g
:
:
U
n
u
s
e
d
;
d
o
u
b
l
e D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
(
U
n
u
s
e
d
, d
o
u
b
l
e x
, d
o
u
b
l
e y
) {
r
e
t
u
r
n s
q
r
t
(
x
*
x + y
*
y
)
;
}
.
.
.
E
X
E
P
C
T
_
C
A
L
L
(
m
o
c
k
, F
o
o
(
"
a
b
c
"
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
)
)
;
E
X
E
P
C
T
_
C
A
L
L
(
m
o
c
k
, B
a
r
(
5
, _
, _
)
)
.
W
i
l
l
O
n
c
e
(
I
n
v
o
k
e
(
D
i
s
t
a
n
c
e
T
o
O
r
i
g
i
n
)
)
;
Sharing Actions
Just like matchers, a Google Mock action object consists of a pointer to a refcounted implementation object. Therefore copying actions is also
allowed and very efficient. When the last action that references the implementation object dies, the implementation object will be deleted.
If you have some complex action that you want to use again and again, you may not have to build it from scratch everytime. If the action doesn't
have an internal state (i.e. if it always does the same thing no matter how many times it has been called), you can assign it to an action variable
and use that variable repeatedly. For example:
A
c
t
i
o
n
 s
e
t
_
f
l
a
g = D
o
A
l
l
(
S
e
t
A
r
g
P
o
i
n
t
e
e
<
0
>
(
5
)
,
R
e
t
u
r
n
(
t
r
u
e
)
)
;
.
.
. u
s
e s
e
t
_
f
l
a
g i
n .
W
i
l
l
O
n
c
e
(
) a
n
d .
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
) .
.
.
However, if the action has its own state, you may be surprised if you share the action object. Suppose you have an action factory
I
n
c
r
e
m
e
n
t
C
o
u
n
t
e
r
(
i
n
i
t
)which creates an action that increments and returns a counter whose initial value is i
n
i
t
, using two actions created

from the same expression and using a shared action will exihibit different behaviors. Example:
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
I
n
c
r
e
m
e
n
t
C
o
u
n
t
e
r
(
0
)
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
I
n
c
r
e
m
e
n
t
C
o
u
n
t
e
r
(
0
)
)
;
f
o
o
.
D
o
T
h
i
s
(
)
; /
/ R
e
t
u
r
n
s 1
.
f
o
o
.
D
o
T
h
i
s
(
)
; /
/ R
e
t
u
r
n
s 2
.
f
o
o
.
D
o
T
h
a
t
(
)
; /
/ R
e
t
u
r
n
s 1 - B
l
a
h
(
) u
s
e
s a d
i
f
f
e
r
e
n
t
/
/ c
o
u
n
t
e
r t
h
a
n B
a
r
(
)
'
s
.
versus
A
c
t
i
o
n
 i
n
c
r
e
m
e
n
t = I
n
c
r
e
m
e
n
t
C
o
u
n
t
e
r
(
0
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
i
s
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
i
n
c
r
e
m
e
n
t
)
;
E
X
P
E
C
T
_
C
A
L
L
(
f
o
o
, D
o
T
h
a
t
(
)
)
.
W
i
l
l
R
e
p
e
a
t
e
d
l
y
(
i
n
c
r
e
m
e
n
t
)
;
f
o
o
.
D
o
T
h
i
s
(
)
; /
/ R
e
t
u
r
n
s 1
.
f
o
o
.
D
o
T
h
i
s
(
)
; /
/ R
e
t
u
r
n
s 2
.
f
o
o
.
D
o
T
h
a
t
(
)
; /
/ R
e
t
u
r
n
s 3 - t
h
e c
o
u
n
t
e
r i
s s
h
a
r
e
d
.
Misc Recipes on Using Google Mock
Making the Compilation Faster
Believe it or not, the vast majority of the time spent on compiling a mock class is in generating its constructor and destructor, as they perform
nontrivial tasks (e.g. verification of the expectations). What's more, mock methods with different signatures have different types and thus their
constructors/destructors need to be generated by the compiler separately. As a result, if you mock many different types of methods, compiling
your mock class can get really slow.
If you are experiencing slow compilation, you can move the definition of your mock class' constructor and destructor out of the class body and
into a .
c
p
pfile. This way, even if you #
i
n
c
l
u
d
eyour mock class in N files, the compiler only needs to generate its constructor and destructor
once, resulting in a much faster compilation.
Let's illustrate the idea using an example. Here's the definition of a mock class before applying this recipe:
/
/ F
i
l
e m
o
c
k
_
f
o
o
.
h
.
.
.
.
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
/
/ S
i
n
c
e w
e d
o
n
'
t d
e
c
l
a
r
e t
h
e c
o
n
s
t
r
u
c
t
o
r o
r t
h
e d
e
s
t
r
u
c
t
o
r
,
/
/ t
h
e c
o
m
p
i
l
e
r w
i
l
l g
e
n
e
r
a
t
e t
h
e
m i
n e
v
e
r
y t
r
a
n
s
l
a
t
i
o
n u
n
i
t
/
/ w
h
e
r
e t
h
i
s m
o
c
k c
l
a
s
s i
s u
s
e
d
.
M
O
C
K
_
M
E
T
H
O
D
0
(
D
o
T
h
i
s
, i
n
t
(
)
)
;
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
a
t
, b
o
o
l
(
c
o
n
s
t c
h
a
r
* s
t
r
)
)
;
.
.
. m
o
r
e m
o
c
k m
e
t
h
o
d
s .
.
.
}
;
After the change, it would look like:
/
/ F
i
l
e m
o
c
k
_
f
o
o
.
h
.
.
.
.
c
l
a
s
s M
o
c
k
F
o
o : p
u
b
l
i
c F
o
o {
p
u
b
l
i
c
:
/
/ T
h
e c
o
n
s
t
r
u
c
t
o
r a
n
d d
e
s
t
r
u
c
t
o
r a
r
e d
e
c
l
a
r
e
d
, b
u
t n
o
t d
e
f
i
n
e
d
, h
e
r
e
.
M
o
c
k
F
o
o
(
)
;
v
i
r
t
u
a
l ~
M
o
c
k
F
o
o
(
)
;
M
O
C
K
_
M
E
T
H
O
D
0
(
D
o
T
h
i
s
, i
n
t
(
)
)
;
M
O
C
K
_
M
E
T
H
O
D
1
(
D
o
T
h
a
t
, b
o
o
l
(
c
o
n
s
t c
h
a
r
* s
t
r
)
)
;
.
.
. m
o
r
e m
o
c
k m
e
t
h
o
d
s .
.
.
}
;
and
/
/ F
i
l
e m
o
c
k
_
f
o
o
.
c
p
p
.
#
i
n
c
l
u
d
e "
p
a
t
h
/
t
o
/
m
o
c
k
_
f
o
o
.
h
"

gmock-cookbook.pdf

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gmock-cookbook.pdf