There is not really right or wrong answer and we have decided to use the Assert test as it test the end result.
I took the TDD approach and re-implemented/analysed as below.
- Start with a failing test (to simplify the code I removed the Repository from both test and the sut)
//AssertTest
[TestMethod]
public void GetErrorList_WhenParameterIsEmpty_ReturnsExpectedErrorCodes1()
{
//Arrange
const string expectedErrorCodes = "200, 201";
var stubErrorRepo = new Mock<IErrorProvider>();
stubErrorRepo.Setup(e => e.BuildErrorMessage(expectedErrorCodes)).Returns(new ErrorInfo() { ErrorCodes = expectedErrorCodes });
var sut = new Class1(stubErrorRepo.Object);
//Act
var result = sut.GetErrorList();
//Assert
Assert.AreEqual(expectedErrorCodes, result.Single().ErrorCodes);
}
//SUT
public IEnumerable<ErrorInfo> GetErrorList(int id)
{
yield return new ErrorInfo();
}
As you would expect the test fail.
Now if write enough production code to make this test pass.
public IEnumerable<ErrorInfo> GetErrorList()
{
yield return _errorProvider.BuildErrorMessage("200, 201");
}
The VerifyTest would still fail for the above SUT.
//VerifyTest
[TestMethod]
public void GetErrorList_WhenParameterIsEmpty_ReturnsExpectedErrorCodes2()
{
//Arrange
var stubErrorMock = new Mock<IErrorProvider>();
var sut = new Class1(stubErrorMock.Object);
//Act
sut.GetErrorList();
//Verify
string verifiableErrorCodes = "200, 201";
stubErrorMock.Verify(x => x.BuildErrorMessage(verifiableErrorCodes));
}
However if I want this test to pass, I can write the below production code as below
public IEnumerable<ErrorInfo> GetErrorList()
{
_errorProvider.BuildErrorMessage("200, 201");
return null;
}
Now the VerifyTest passes, but the AssertTest fails.
Both tests are valid in their own ways. However they test different semantics. AssertTest test whether the end result contains the correct error codes. Verify test ensures the method is called with the correct error codes. It is important to note that the end value of the Assert test is based on the setup method "match" provided by the Moq framework. In other words the setup dictates what the end result would be. AssertTest would fail if the setup is configured incorrectly or the production code uses error codes that does not match the setup configuration.
It is preferred to use the AssertTest as it test the end result.