ISTQB / ISEB Foundation Exam Practice - 4

1. Chapter 4
Software Testing
ISTQB / ISEB Foundation Exam Practice
1 Principles 2 Lifecycle 3 Static testing
4 Dynamic test
5 Management 6 Tools
techniques
Dynamic Testing Techniques

2. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Contents
What is a testing technique?
Black and White box testing
Black box test techniques
White box test techniques
Error Guessing

3. Why dynamic test techniques?
 Exhaustive testing (use of all possible inputs
and conditions) is impractical
- must use a subset of all possible test cases
- must have high probability of detecting faults
 Need thought processes that help us select
test cases more intelligently
- test case design techniques are such thought
processes

4. What is a testing technique?
 a procedure for selecting or designing tests
 based on a structural or functional model of
the software
 successful at finding faults
 'best' practice
 a way of deriving good test cases
 a way of objectively measuring a test effort
Testing should be rigorous, thorough and systematic

5. Advantages of techniques
 Different people: similar probability find faults
- gain some independence of thought
 Effective testing: find more faults
- focus attention on specific types of fault
- know you're testing the right thing
 Efficient testing: find faults with less effort
- avoid duplication
- systematic techniques are measurable
Using techniques makes testing much more effective

6. Measurement
 Objective assessment of thoroughness of
testing (with respect to use of each technique)
- useful for comparison of one test effort to another
 E.g.
Project A Project B
60% Equivalence 40% Equivalence
partitions partitions
50% Boundaries 45% Boundaries
75% Branches 60% Branches

7. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Contents
What is a testing technique?
Black and White box testing
Black box test techniques
White box test techniques
Error Guessing

8. Three types of systematic technique
Static (non-execution)
• examination of documentation,
source code listings, etc.
Functional (Black Box)
• based on behaviour /
functionality of software
Structural (White Box)
• based on structure
of software

9. Some test techniques
Static Dynamic
Reviews etc.
Static Analysis
Behavioural
Inspection
Walkthroughs Structural Non-functional Functional
Desk-checking etc.
etc.
Equivalence
Control Usability Partitioning
Data Flow
Flow Performance
etc. Boundary
Value Analysis
etc.
Statement
Symbolic Cause-Effect Graphing
Execution Branch/Decision Arcs
Random
Definition Branch Condition LCSAJ
-Use State Transition
Branch Condition
Combination

10. Black box versus white box?
Black box appropriate Acceptance
at all levels but
dominates higher
levels of testing System
White box used
predominately Integration
at lower levels
to compliment
Component
black box

11. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Contents
What is a testing technique?
Black and White box testing
Black box test techniques
White box test techniques
Error Guessing

12. Black Box test design and
measurement techniques
 Techniques defined in BS 7925-2
- Equivalence partitioning
- Boundary value analysis Also a measurement
technique?
- State transition testing = Yes
- Cause-effect graphing = No
- Syntax testing
- Random testing
 Also defines how to specify other techniques

13. Equivalence partitioning (EP)
- divide (partition) the inputs, outputs, etc. into areas
which are the same (equivalent)
- assumption: if one value works, all will work
- one from each partition better than all from one
invalid valid invalid
0 1 100 101

14. Boundary value analysis (BVA)
- faults tend to lurk near boundaries
- good place to look for faults
- test values on both sides of boundaries
invalid valid invalid
0 1 100 101

15. Example: Loan application
2-64 chars.
Customer Name
Account number 6 digits, 1st
non-zero
Loan amount requested
Term of loan £500 to £9000
Monthly repayment
1 to 30 years
Term:
Minimum £10
Repayment:
Interest rate:
Total paid back:

16. Customer name
Number of characters:
1 2 64 65
invalid valid invalid
Valid characters: A-Z
Any
-‟ a-z
space other
Conditions Valid Invalid Valid Invalid
Partitions Partitions Boundaries Boundaries
Customer 2 to 64 chars < 2 chars 2 chars 1 chars
name valid chars > 64 chars 64 chars 65 chars
invalid chars 0 chars

17. Account number
valid: non-zero
first character:
invalid: zero
number of digits: 5 6 7
invalid invalid
valid
Conditions Valid Invalid Valid Invalid
Partitions Partitions Boundaries Boundaries
Account 6 digits < 6 digits 100000 5 digits
number 1st non-zero > 6 digits 999999 7 digits
1st digit = 0 0 digits
non-digit

18. Loan amount
499 500 9000 9001
invalid valid invalid
Conditions Valid Invalid Valid Invalid
Partitions Partitions Boundaries Boundaries
Loan 500 - 9000 < 500 500 499
amount >9000 9000 9001
0
non-numeric
null

19. Condition template
Conditions Valid Tag Invalid Tag Valid Tag Invalid Tag
Partitions Partitions Boundaries Boundaries
Customer 2 - 64 chars V1 < 2 chars X1 2 chars B1 1 char D1
name valid chars V2 > 64 chars X2 64 chars B2 65 chars D2
invalid char X3 0 chars D3
Account 6 digits V3 < 6 digits X4 100000 B3 5 digits D4
number 1st non-zero V4 > 6 digits X5 999999 B4 7 digits D5
st
1 digit = 0 X6 0 digits D6
non-digit X7
Loan 500 - 9000 V5 < 500 X8 500 B5 499 D7
amount >9000 X9 9000 B6 9001 D8
0 X10
non-integer X11
null X12

20. Design test cases
Test Description Expected Outcome New Tags
Case Covered
1 Name: John Smith Term: 3 years V1, V2,
Acc no: 123456 Repayment: 79.86 V3, V4,
Loan: 2500 Interest rate: 10% V5 .....
Term: 3 years Total paid: 2874.96
2 Name: AB Term: 1 year B1, B3,
Acc no: 100000 Repayment: 44.80 B5, .....
Loan: 500 Interest rate: 7.5%
Term: 1 year Total paid: 537.60

21. Why do both EP and BVA?
 If you do boundaries only, you have covered
all the partitions as well
- technically correct and may be OK if everything
works correctly!
- if the test fails, is the whole partition wrong, or is a
boundary in the wrong place - have to test mid-
partition anyway
- testing only extremes may not give confidence for
typical use scenarios (especially for users)
- boundaries may be harder (more costly) to set up

22. Test objectives?
Condition Valid Tag Invalid Tag Valid Tag Invalid Tag
Partition Partition Boundary Boundary
 For a thorough approach: VP, IP, VB, IB
 Under time pressure, depends on your test objective
- minimal user-confidence: VP only?
- maximum fault finding: VB first (plus IB?)

23. Decision tables
 explore combinations of inputs, situations or
events,
 it is very easy to overlook specific
combinations of input
 start by expressing the input conditions of
interest so that they are either TRUE or FALSE
– record found – policy expired
– file exists – account in credit
– code valid – due date > current date

24. Example: student access
A university computer system allows students
an allocation of disc space depending on their
projects.
If they have used all their allotted space, they
are only allowed restricted access, i.e. to
delete files, not to create them. This is
assuming they have logged on with a valid
username and password.
What are the input and output conditions?

25. List the input and output conditions
• list the „input Input Conditions
conditions‟ in the first Valid username
column of the table Valid password
Account in credit
• list the „output Output Conditions
conditions‟ under the Login accepted
input conditions Restricted access

26. Determine input combinations
 add columns to the table for each unique
combination of input conditions.
 each entry in the table may be either „T‟ for
true, „F‟ for false.
Input Conditions
Valid username T T T T F F F F
Valid password T T F F T T F F
Account in credit T F T F T F T F

27. Rationalise input combinations
 some combinations may be impossible or not
of interest
 some combinations may be „equivalent‟
 use a hyphen to denote “don‟t care”
Input Conditions
Valid username F T T T
Valid password - F T T
Account in credit - - F T

28. Complete the table
 determine the expected output conditions for
each combination of input conditions
Input Conditions
Valid username F T T T
Valid password - F T T
Account in credit - - F T
Output Conditions
Login accepted F F T T
Restricted access - - T F

29. Determine test case groups
 each column is at least one test case
Input Conditions
Valid username F T T T
Valid password - F T T
Account in credit - - F T
Output Conditions
Login accepted F F T T
Restricted access - - T F
Tags A B C D

30. Design test cases
 usually one test case for each column but can
be none or several
Test Description Expected Outcome Tag
1 Username BrbU Invalid username A
2 Username Invalid username A
usernametoolong
3 Username BobU Invalid password B
Password abcd
4 Valid user, no disc Restricted access C
space
5 Valid user with disc Unrestricted access D
space

31. Rationalising outputs
 if outputs or effects are mutually exclusive,
I.e. T occurs in only one place in each column,
we can combine them
 for example:
X T F F
is equivalent to:
Y F T F
Z F F T Output X Y Z

32. Rationalising dangers
 rationalising is based on assumptions
 assumptions may be wrong!
 assumptions should be stated
 assumptions may change over time
 be aware of the dangers
- filling in the full table may find errors which will be
missed if you rationalise
- it is possible to rationalise too far

33. Extending decision tables
 Entries can be more than just „true‟ or „false‟
- completing table needs to be done carefully
- rationalising becomes more important
 E.g.
Code = 1, 2, or 3 1 1 1 1 2 2 2 2 3 3 3 3
Exp.date < now T T F F T T F F T T F F
Class A product T F T F T F T F T F T F

34. Decision Tables in relation to EP and
BVA
Input value Output value
FALSE
TRUE

35. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Contents
What is a testing technique?
Black and White box testing
Black box test techniques
White box test techniques
Error Guessing

36. White Box test design and
measurement techniques
 Techniques defined in BS 7925-2
- Statement testing Also a measurement
technique?
- Branch / Decision testing = Yes
- Data flow testing = No
- Branch condition testing
- Branch condition combination testing
- Modified condition decision testing
- LCSAJ testing
 Also defines how to specify other techniques

37. Using structural coverage
Spec Enough
Software tests?
Tests
Results OK?
What's
covered?
More tests Coverage OK?
Stronger structural
techniques (different
structural elements)
Increasing coverage

38. The test coverage trap
Function exercised, better testing
insufficient structure
Functional
testedness
Structure exercised,
insufficient function
% Statement % Decision % Condition
Combination
Structural testedness
100% coverage does Coverage is not
not mean 100% tested! Thoroughness

39. Statement coverage
Statement coverage is normally measured
by a software tool.
 percentage of executable statements
exercised by a test suite
number of statements exercised ?
=
total number of statements
 example:
- program has 100 statements
- tests exercise 87 statements
- statement coverage = 87%
Typical ad hoc testing achieves 60 - 75%

40. Example of statement coverage
1 read(a) Test Input Expected
2 IF a > 6 THEN case output
3 b=a 1 7 7
4 ENDIF
5 print b
As all 5 statements are „covered‟ by
this test case, we have achieved
Statement 100% statement coverage
numbers

41. Decision coverage
Decision coverage is normally measured
by a software tool.
(Branch coverage)
 percentage of decision outcomes
exercised by a test suite
number of decisions outcomes exercised False
= ?
total number of decision outcomes
True
 example:
- program has 120 decision outcomes
- tests exercise 60 decision outcomes
- decision coverage = 50%
Typical ad hoc testing achieves 40 - 60%

42. Paths through code 1234
12 12 123
?
? ? ? ?
?

43. Paths through code with loops
1 2 3 4 5 6 7 8 ….
for as many times as it
is possible to go round
? the loop (this can be
unlimited, i.e. infinite)

44. Wait
Example 1
Wait for card to be inserted Yes
Valid Display
IF card is a valid card THEN card? “Enter..
display “Enter PIN number” No
IF PIN is valid THEN
Reject Valid Yes Select
select transaction PIN?
card trans...
ELSE (otherwise) No
display “PIN invalid”
ELSE (otherwise) Display
“PIN in..
reject card
End
End

45. Example 2 Read
Read A Yes Yes
A>0 A=21
IF A > 0 THEN
IF A = 21 THEN No No
Print
Print “Key”
ENDIF
ENDIF
End
3
- Cyclomatic complexity: _____
- Minimum tests to achieve:
1
• Statement coverage: ______
• Branch coverage: _____
3

46. Example 3 Read
Read A Yes No
Read B A>0 B=0 Print
IF A > 0 THEN No Yes
Yes
IF B = 0 THEN Print A>21 Print
Print “No values”
No
ELSE
Print B
IF A > 21 THEN End
Print A 4
- Cyclomatic complexity: _____
ENDIF
ENDIF - Minimum tests to achieve:
ENDIF 2
• Statement coverage: ______
• Branch coverage: _____
4

47. Yes
Read A<0 Print
Example 4 No
Read A Note: there Print
Read B are 4 paths
IF A < 0 THEN Yes
Print “A negative” B<0 Print
ELSE No
Print “A positive” Print
ENDIF
IF B < 0 THEN
Print “B negative” End
ELSE 3
- Cyclomatic complexity: _____
Print “B positive”
ENDIF - Minimum tests to achieve:
• Statement coverage: ______
2
• Branch coverage: _____
2

48. Yes
Read A<0 Print
Example 5 No
Read A
Read B Yes
B<0 Print
IF A < 0 THEN
No
Print “A negative”
ENDIF
IF B < 0 THEN End
Print “B negative”
ENDIF
3
- Cyclomatic complexity: _____
- Minimum tests to achieve:
1
• Statement coverage: ______
• Branch coverage: _____
2

49. Yes
Read A<0 Print
Example 6 No
Read A
IF A < 0 THEN Yes
A>0 Print
Print “A negative”
No
ENDIF
IF A > 0 THEN
Print “A positive” End
ENDIF
3
- Cyclomatic complexity: _____
- Minimum tests to achieve:
2
• Statement coverage: ______
• Branch coverage: _____
2

50. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Contents
What is a testing technique?
Black and White box testing
Black box test techniques
White box test techniques
Error Guessing

51. Non-systematic test techniques
 Trial and error / Ad hoc
 Error guessing / Experience-driven
 User Testing
 Unscripted Testing
A testing approach that is only
rigorous, thorough and systematic
is incomplete

52. Error-Guessing
 always worth including
 after systematic techniques have been used
 can find some faults that systematic
techniques can miss
 a „mopping up‟ approach
 supplements systematic techniques
Not a good approach to start testing with

53. Error Guessing: deriving test cases
 Consider:
- past failures
- intuition
- experience
- brain storming
- “What is the craziest thing we can do?”

54. 1 2 3 ISTQB / ISEB Foundation Exam Practice
4 5 6
Dynamic Testing Techniques
Summary: Key Points
Test techniques are „best practice‟: help to find faults
Black Box techniques are based on behaviour
White Box techniques are based on structure
Error Guessing supplements systematic techniques