Unit testing basics with NUnit and Visual Studio

Technical reasons
 Tests encourage better design sooner
 Tests are the best documentation
 Tests are your safety net
 Every day use
 Major refactoring freedom

Test Types
 Unit Testing
 Tests an atomic unit of code, such as a method
 Integration Testing
 Tests two or more software modules as a group
 User Acceptance Testing
 Tests performed by end users to validate specific features
 TDD Test
 Look like a unit test, feels like an user acceptance test

Unit Testing Defined
 A unit test is a piece of code that invokes the
method or class being tested and then checks
some assumptions about the logical behavior of
that method or class. A unit test is almost always
written using a unit-testing framework.
The Art of Unit Testing by Roy Osherove

Unit vs. Integration Testing
 Unit tests exercise and test a single
piece of code
 Integration tests exercise and test many
units of code that work together as a
whole

Code to Unit Test
 Unit tests should target logical code
 Logical code is defined as any piece of code
that contains any type of decision making
logic such as IF statements, loops, switch
statements, calculations etc.

Properties of a Good Unit Test
 It is Automated and Repeatable
 It is Easy to Implement
 It Can Be Run in the Future
 It Can Be Run by Anyone
 It Can Run at the Push of a Button
 It Runs Quickly

Test Project Creation Guidelines
 Demo and setup

Test Project Creation Guidelines
 Create separate test projects for unit tests and
integration tests. This will allow for calling unit
tests from the build process in the future
 Test project naming convention:
 [Project Name].UnitTests
 [Project Name].IntegrationTests

Test Class Guidelines
 Each class being tested should have its own test
class defined (the one-test-class-per-class pattern)
 Create utility methods if multiple tests need the same
functionality
 Test class naming convention:
 [Class Name]Tests.cs
where Class Name is the name of the class being
tested.

Test Method Guidelines
 Each public method exposed by the class under
test should be tested
// Configure/Setup
// Action
// Assert
Note: you can test Internal methods (if required). Use
InternalsVisibleTo[<Project>.UnitTests] attribute in AssemblyInfo.
 Test method naming convention:
 [Method Name]_[Scenario]_[ExpectedBehavior]
Examples:
ValidateCreditCard_InvalidExpiryDate_ThrowsException()
ValidateCreditCard_InvalidAddress_ThrowsException()

NUNIT Test Framework Attributes
Define class as a TestClass
[TestFixture]
public class FileManagerTests { }
Define a test method test a single method and expected
behavior
[Test]
public void IsValidFileName_InvalidFilePath_ThrowException(){ }
Use setup attribute to call required code before each test in the
class. For e.g. InitializeConfiguration()

Test Project Structure
 The test project, class, and method guidelines
allow us to do the following:
 Look at a project and find all related tests
 Look at a class and find all related tests
 Look at a class method and find all related tests

Unit Testing Techniques
 An external dependency is an object in the
system under test over which you have no
control.
 External dependencies need to be “faked”. It is
necessary to fake those dependencies to make
sure the scope of the code being tested is
limited to the system under test.

Unit Testing Techniques
 Stub:
 A controllable replacement for an existing external dependency in the
system.
 It allows to test code without dealing with dependencies directly, since
those dependencies are effectively simulated.
 can never fail a test
 Mock:
 A fake object in the system that decides whether the unit test passed or
failed.
 The unit test verifies the state of the mock object to determine success or
failure.
 may result in failed tests.
 State of the object would be checked as asserts gets created against
them.

.. And Dependency injection
 Decouple the components by injecting
them via constructors.
 Increase the testability.

Mocks and Stubs – Things to Consider
 Writing mocks and stubs takes time, so keep
them as simple as possible
 Focus on Reusability
 Inject stub/mocks to replace the dependency
component.
 Use available libraries e.g. RhinoMocks

Test Code Coverage
 Above 95% code coverage
 Do not confuse with covering entire assembly .
 Method level would be sufficient
 Use tools(Inbuilt or third party).

Hallmarks of Quality Tests
 Trustworthiness – Developers will want to run
trustworthy tests, which are tests whose results
are reliable
 Maintainability – Non-maintainable tests are
short-lived. The more focused and short the test
methods, the more maintainable.
 Readability - If the tests are not easily
readable, they will most likely be less
trustworthy and less maintainable

Signs of Trustworthy Tests
 When a test passes, your first reaction is not to
say “I’ll step through the debugger just to
make sure”
 When a test fails, your first reaction is not to
say, “Well, that does not mean the code is
not working”
 When you run the tests, your first reaction is not
to say “Yes but, what about this scenario?”
due to lack of coverage

Why UnitTests?
 Saves your time of debugging via print
statements, traces or VS debugger.
 Saves other’s time from stepping
through your code to ensure it’s working.
 Reduce bugs in early stage
 Better design

Resources
 Nunit
 http://www.nunit.org
 Code Coverage Overview
 http://msdn.microsoft.com/en-
us/library/cc667391(v=VS.90).aspx
 Rhino Mocks
 http://ayende.com/blog/tags/rhino-mocks

 Blog – www.cshandler.com
About me
Amit Choudhary
Microsoft MVP Visual C#
Twitter – @vendettamit

Unit testing basics with NUnit and Visual Studio

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