Using ExtensionMethods with Moq to Make Your Unit Tests More Readable

As you may have noticed from last week’s post I’ve been doing a lot of Unit Testing work recently. The product I’m working on is huge and very complex and this makes Unit Testing (as well as general coding) a real challenge. I’ve decided to write a more technical post this week focusing on a trick I’ve found which I believe really helps improve the quality of your tests.

One of the tools we’re using is Moq, a mocking framework (much like RhinoMocks or NSubstitute (one I’ve not used but comes recommended)).

One of the biggest challenges developers face when creating Unit Tests is maintaining readability as the test grows. Consider the following typical test

[Test]
public void TypicalTestSetup()
{
  // Arrange
  var mock = new Mock<IDataAccess>();
  mock.Setup(x => x.GetIDOfRowWithGuid(It.IsAny<Guid>())).Returns(12);
  mock.Setup(x => x.GetValueFromDatabase()).Returns(1701);
  mock.Setup(x => x.SaveValue(73)).Returns(36);
  var sut = new BusinessLogic(mock.Object); 

  // Act
  var result = sut.DoWork(7);

  // Assert
  Assert.Equals(42, result);
}

As the mock is an object there’s no reason you can’t create ExtensionMethods for them. If I create the following method

 

/// <summary>
/// Sets up the method GetIDOfRowWithGuid to return the value given
/// </summary>
public static void SetupGetIDOfRowWithGuid(this Mock<IDataAccess> mock, int value)
{
  mock.Setup(x => x.GetIDOfRowWithGuid(It.IsAny<Guid>())).Returns(value);
}

 This allows us to call the setup code much more succinctly

mock.SetupGetIDOfRowWithGuid(12);

Personally I also like to return the mock as part of the ExtensionMethod

/// <summary>
/// Sets up the method GetIDOfRowWithGuid to return the value given
/// </summary>
public static Mock<IDataAccess> SetupGetIDOfRowWithGuid(this Mock<IDataAccess> mock, int value)
{
  mock.Setup(x => x.GetIDOfRowWithGuid(It.IsAny<Guid>())).Returns(value);
  return mock;
}

Because this allows you to create more more fluent style setup instructions.

// Arrange
var mock = new Mock<IDataAccess>()
  .SetupGetIDOfRowWithGuid(12)
  .SetupGetValueFromDatabase(1701)
  .SetupSaveValue(73, 36);
var sut = new BusinessLogic(mock.Object);			

This, in my opinion is far more readable, simplifies your setup and can be used to create powerful, reusable setups and verifies.

Have you used ExtensionMethods with mocks? What other tips and tricks do you use to keep your Unit Tests in order?

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