A good basis for unit testing

Over time, one developers techniques and habits that “just work”. In this post, I would like to share with you a set of base classes that I’ve been using and refining over time. They make my Unit Test writing a little more efficient and easy on the eyes.

The base of the base

I often start a new software project by setting up some form of base unit test class with functionality that I know I will be using, such as using embedded resource documents, various kinds of verifiers, test names etc. I usually name this class “BaseUnitTest”. This blog post will not be focussing on this base of bases, but to give you an idea, this is roughly how it starts out.

public class BaseUnitTest
{
    private Assembly _testAssembly;
    public EmbeddedResourceManger ResourceManager { get; internal set; }
    public IoVerificationManager IoVerifier { get; internal set; }

    public BaseUnitTest ()
    {
        _testAssembly = Assembly.GetCallingAssembly();
        ResourceManager = new EmbeddedResourceManger(_testAssembly);

        IoVerifier = new IoVerificationManager();
    }
}

I usually add on methods to this class in the form of Verfiers of different sorts. A handy base class for your Unit  Tests is not the scope of this blog though…

Wrapping AutoMocking and Instance creation with BasedOn<T>

Now follows the real nugget. A base class for your unit tests that uses StuctureMap’s AutoMocker to construct a nice, testable innstance of the class under test.

[TestClass]
public abstract class BasedOn<TInstance> : BaseUnitTest where TInstance : class
{
    public MoqAutoMocker<TInstance> AutoMocker { get; internal set; }
    public TInstance Instance { get; internal set; }

    [TestInitialize]
    public void RunBeforeEachTest() 
    {
        AutoMocker = new MoqAutoMocker<TInstance>();

        OverrideMocks();

        Instance = AutoMocker.ClassUnderTest;

        ExecuteBeforeEachTest();
    }

    public Mock<TInterface> GetMockFor<TInterface>() where TInterface : class
    {
        return Mock.Get(AutoMocker.Get<TInterface>());
    }

    /// <summary>
    /// Use this from your OverrideMocks() method so that all replacements are made before
    /// the Instance is created
    /// </summary>
    public void Replace<TInterface>(TInterface with) where TInterface: class
    {
        AutoMocker.Inject<TInterface>(with);
    }

    public virtual void OverrideMocks()
    {
    }

    public virtual void ExecuteBeforeEachTest()
    {
    }
}

How it works

The BasedOn<T> class defines an AutoMocker for the class that will be tested as well as a member named ‘Instance’ that is used in the unit tests. The method RunBeforeEachTest() is attributed with [TestInialize] so that it will execute prior to each unit test.

Note: Because this attribute is used in the baseclass, you cannot re-attribute any method in your derived unit test class. That is why there is a method named ExecuteBeforeEachTest() that you can override to accomodate your Unit testing needs.

If you need to prepare a special Mock or stub into the class you are testing, you can override the method OverrideMocks() in your unit test class – this method is executed just before the Instance member is created. The method Replace<T>(T with) is meant to be used for this very purpose.

Example of use

The class PersonManager is a business layer service that handles Person objects. In the following example, we are setting up a Unit test to ensure that person objects that do not have surnames cannot be updated. Using the BasedOn<T> base class:

[TestClass]
public class PersonManagerTests : BasedOn<PersonManager>
{
    [TestMethod]
    public void UpdatePerson_PersonHasNoLastName_DoesNotInvokeRepositoryUpdate()
    {
        // Arrange
        var testPerson = new Person();

        // Act
        Instance.UpdatePerson(testPerson);

        // Assert
        var repoMock = GetMockFor<IPersonRepository>();
        repoMock.Verify(o => o.Update(testPerson), Times.Never());
    }
}

In the next example, I am preparing the repository to throw an exception to verify

that an exception uses the logger interface:

[TestMethod]
public void Create_RepositoryThrowsException_ErrorMessageIsLogged()
{
    // Arrange
    var somePerson       = new Person();
    string exceptionText = "Something really bad just happened";
    var someException    = new Exception(exceptionText);
    var repoMock         = GetMockFor<IPersonRepository>();

    repoMock.Setup(o => o.Create(somePerson)).Throws(someException);

    // Act
    Instance.Create(somePerson);

    // Assert
    var loggerMock = GetMockFor<ILogger>();
    loggerMock.Verify(o => o.LogException(exceptionText), Times.Once());
}

The magic performed by AutoMocker combined with a relatively simple base class has helped me immensly in making my tests more readable – and for others to read! At the time of this writing, AutoMocker supports Moq, Castle, and TypeMock.

For those classes that you do not want automocked, you can always bypass the BasedOn<T> class and inherit the BaseUnitTest directly for access to the test helper methods and verifiers.