Simple mocking library for .NET

1. MOCKING WITH MOQ
A look at mocking objects
with the Moq framework
By: Mohamed Elkhodary

2. YOUR EXPECTATIONS

3. TEST DRIVEN DEVELOPMENT
If it's worth building, it's worth testing.
If it's not worth testing, why are you wasting your time working
on it?

4. TEST DRIVEN DEVELOPMENT

5. THE PROBLEM

6. SOLUTION

7. INTRODUCTION What is mocking?

8. TERMINOLOGIES
o Mocks used to define expectations. Like expecting that method A()
to be called with defined parameters. Mocks record and verify such
expectations.
o Stubs do not record or verify expectations, but rather allow us to
“replace” the behavior and state of the “fake” object in order to utilize
a test scenario.
o Dummy objects are passed around but never actually used. Usually
they are just used to fill parameter lists.

9. MOCKING AN OBJECT
o Mock objects are simulated
objects that mimic the behavior
of real objects in controlled
ways.
o A programmer typically creates
a mock object to test the
behavior of some other object.

10. REASONS FOR USE
o The object supplies non-deterministic results (e.g., the current time
or the current temperature).
o It has states that are difficult to create or reproduce (e.g., a network
error).
o It is slow (e.g., a complete database, which would have to be
initialized before the test).
o It does not yet exist or may change behavior.
o Testing it is out of current scope (External component).
o Focus on SUT without worrying about its dependencies.

11. WHAT DOES A MOCKING
FRAMEWORK DO?
1. Create fake objects.
2. Set behavior of fake objects.
3. Verify method was called.
4. And much more .

12. STEPS OF MOCKING
Arrange Act Assert

13. RULE OF THUMB
Apply mocks only on Unit Tests, not
Integration Tests

14. TECHNICAL DETAILS
o Mock objects have the same interface as the real objects they mimic,
allowing a client object to remain unaware of whether it is using a
real object or a mock object.
o Many available mock object frameworks allow the programmer to
specify which, and in what order, methods will be invoked on a mock
object and what parameters will be passed to them, as well as what
values will be returned.
o Behavior of a complex object such as a network socket can be
mimicked by a mock object, allowing the programmer to discover
whether the object being tested responds appropriately to the wide
variety of states such mock objects may be in.

15. HAND ROLLED MOCK Example

16. TRY IT | CUSTOMER SERVICE
o This service dependent on:
o CustomerAdressBuilder.
o Has a method ‘From’ whose input parameter is a customer command and return an address as a string.
o CustomerRepository.
o Can save a customer object on the persistence storage.
o Get mailing address to customer from CustomerAddressBuilder.
o Throws InvalidCustomerMailingAddressException if mailing address
is null.
o Assign mailing address to customer.
o Persist customer in CustomerRepository.

17. MOQ Code samples

18. 2) SIMPLE MOCK – WATCH USING
MOQ
o Create Single Customer
o Input : CustomerCreateCommand.
o It has to:
oCreate a customer object.
o Persist it on the respository.

19. 2) SIMPLE MOCK– TRY IT
oCreate Bulk of Customers
o Input : List of CustomerCreateCommand.
o It has to:
oCreate a customer object.
o Persist it on the respository.

20. 3) RETURN VALUES – TRY IT
oNotes:
oApply Moq on example of hand rolled mock.
oICustomerAddressBuilder Interface.
o string From(CustomerCreateCommand customercommand);
o Actions:
o Mock address builder to return an Email.
o Write a test method for testing exception if mailing address is
null.
o Verify that CustomerRepository Save method is called.

21. 4) OUTPUT PARAMETERS – TRY IT
oNotes:
oIMailingAddressFactory Interface.
o bool TryParse(string mailingAddress, out MailingAddress result);
o Actions:
o Mock IMailingAddressFactory to return an output parameter.
o Set customer DetailedMailingAddress by the result.
o Verify that CustomerRepository Save method is called.

22. 5) MULTIPLE RETURN VALUES –
TRY IT
o Notes:
oCheck IIdFactory Interface.
oint Create();
o Create method of Customer Service has a list of Customer Create
Commands.
o Set a unique Id for each customer using IIdFactory Interface.
o Persist it on the repository.
o Actions:
o Verify that CustomerRepository Save method is called.
o Verify that Create method is called per command to set
customer Id.

23. 6) ARGUMENT TRACKING – TRY IT
o Notes:
o IFullNameFactory Interface.
ostring From(string firstName, string lastName);
o Set Customer Fullname by result of From method in
IFullNameFactory.
o Persist it on the repository.
o Actions:
o Setup From in IFullNameFactory to get any string values in
both input parameters.
o Verify that both input parameters equals the command
corresponding values.

24. 7) EXECUTION FLOW – TRY IT
Notes:
o IStatusFactory Interface.
o CustomerStatusEnum From(CustomerCreateCommand
createCommand);
o CustomerStatusEnum (Normal, Platinum).
o Set customer status by result from From method in IStatusFactory.
o If Customer status is Platinum, use SaveSpecial in
ICustomerRepository.
o else, use Save in ICustomerRepository.
Actions:
o Setup From in IStatusFactory to return different results.
o Verify that appropriate methods called.

25. 8) PROPERTIES – TRY IT
Notes:
o Check ICustomerRepository Interface.
o Check IApplicationSettings Interface.
o Set Customer Repository Time Zone by Standard name of
current time zone.
Actions:
o Verify ICustomerRepository TimeZone setter.

26. 8) PROPERTIES – TRY IT
Notes:
o Check ICustomerRepository Interface.
o Check IApplicationSettings Interface.
o Set WorkStationId of Customer by WorkStationId of
IApplicationSettings.
Actions:
o Verify IApplicationSettings WorkStationId getter.

27. 8) PROPERTIES – TRY IT
Notes:
o Check ICustomerRepository Interface.
o Check IApplicationSettings Interface.
o Make it harder by using complex property object.
Actions:
o Verify getter of
_applicationSettings.SystemConfiguration.AuditingInformation.WorkStationI
d.

28. 8) PROPERTIES – TRY IT
1. Try using SetupProperty instead of Setup
2. Try setup the property from the exposed object of
mock
3. SetupAllProperties

29. 9) EVENTS – TRY IT
Notes:
o Check IMailingRepository Interface.
o CustomerRepository should subscribe to an Event
NotifySalesTeam.
o Once event is raised, it has to call NewCustomerMessage in
IMailingRepository and pass the event argument.
Actions:
o Verify that NewCustomerMessage is called if event raised.

30. MOQ | ADVANCED TOPICS Samples

31. 1) RECURSIVE MOCKING
Notes:
o Check IMailingAddressFactory Interface.
o Get ICustomerAddressBuilder from
IMailingAddressFactory .
o Set Customer Mailing Address using From method in
ICustomerAddressBuilder.
Actions:
o Verify that From method in ICustomerAddressBuilder is
called.

32. 2) PROTECTED MEMBERS
Notes:
o Check CustomerNameFormatter class.
Actions:
o Verify that RemoveUnderScoreFrom is called.

33. 3) INTERFACES
Notes:
o Check StringSequenceReader class.
Actions:
o Verify that Dispose method is called.

34. EDUWORX Real Example

35. BEST PRACTICES Hints on using TDD

36. THE BAD
o The use of mock objects can closely couple the unit tests to the
actual implementation.
o Test fails even though all mocked object methods still obey the
contract of the previous implementation.
o Over-use of mock objects as part of a suite of unit tests can result
in a dramatic increase in the amount of maintenance.

37. THANK YOU!