Using Moq to verify calls are made in the correct order

Question

I need to test the following method:

CreateOutput(IWriter writer)
{
    writer.Write(type);
    writer.Write(id);
    writer.Write(sender);

    // many more         


        

Answer 1

I suspect that expectedId is not what you expect.

However i'd probably just write my own implementation of IWriter to verify in this case ... probably a lot easier (and easier to change later).

Sorry for no Moq advice directly. I love it, but haven't done this in it.

do you maybe need to add .Verify() at the end of each setup? (That really is a guess though i'm afraid).

Answer 2

My scenario was methods without parameters:

public interface IWriter
    {
    void WriteA ();
    void WriteB ();
    void WriteC ();
    }

So I used Invocations property on the Mock to compare what was called:

var writer = new Mock<IWriter> ();

new SUT (writer.Object).Run ();

Assert.Equal (
    writer.Invocations.Select (invocation => invocation.Method.Name),
    new[]
        {
        nameof (IWriter.WriteB),
        nameof (IWriter.WriteA),
        nameof (IWriter.WriteC),
        });

You could also append the invocation.Arguments to check method calls with parameters.

Also the failure message is more clear than just expected 1 but was 5:

    expected
["WriteB", "WriteA", "WriteC"]
    but was
["WriteA", "WriteB"]

Answer 3

I've managed to get the behaviour I want, but it requires downloading a 3rd-party library from http://dpwhelan.com/blog/software-development/moq-sequences/

The sequence can then be tested using the following:

var mockWriter = new Mock<IWriter>(MockBehavior.Strict);
using (Sequence.Create())
{
    mockWriter.Setup(x => x.Write(expectedType)).InSequence();
    mockWriter.Setup(x => x.Write(expectedId)).InSequence();
    mockWriter.Setup(x => x.Write(expectedSender)).InSequence();
}

I've added this as an answer partly to help document this solution, but I'm still interested in whether something similar could be achieved using Moq 4.0 alone.

I'm not sure if Moq is still in development, but fixing the problem with the MockSequence, or including the moq-sequences extension in Moq would be good to see.

Answer 4

There is bug when using MockSequence on same mock. It definitely will be fixed in later releases of Moq library (you can also fix it manually by changing Moq.MethodCall.Matches implementation).

If you want to use Moq only, then you can verify method call order via callbacks:

int callOrder = 0;
writerMock.Setup(x => x.Write(expectedType)).Callback(() => Assert.That(callOrder++, Is.EqualTo(0)));
writerMock.Setup(x => x.Write(expectedId)).Callback(() => Assert.That(callOrder++, Is.EqualTo(1)));
writerMock.Setup(x => x.Write(expectedSender)).Callback(() => Assert.That(callOrder++, Is.EqualTo(2)));

Answer 5

The simplest solution would be using a Queue:

var expectedParameters = new Queue<string>(new[]{expectedType,expectedId,expectedSender});
mockWriter.Setup(x => x.Write(expectedType))
          .Callback((string s) => Assert.AreEqual(expectedParameters.Dequeue(), s));

Answer 6

I wrote an extension method that will assert based on order of invocation.

public static class MockExtensions
{
  public static void ExpectsInOrder<T>(this Mock<T> mock, params Expression<Action<T>>[] expressions) where T : class
  {
    // All closures have the same instance of sharedCallCount
    var sharedCallCount = 0;
    for (var i = 0; i < expressions.Length; i++)
    {
      // Each closure has it's own instance of expectedCallCount
      var expectedCallCount = i;
      mock.Setup(expressions[i]).Callback(
        () =>
          {
            Assert.AreEqual(expectedCallCount, sharedCallCount);
            sharedCallCount++;
          });
    }
  }
}

It works by taking advantage of the way that closures work with respect to scoped variables. Since there is only one declaration for sharedCallCount, all of the closures will have a reference to the same variable. With expectedCallCount, a new instance is instantiated each iteration of the loop (as opposed to simply using i in the closure). This way, each closure has a copy of i scoped only to itself to compare with the sharedCallCount when the expressions are invoked.

Here's a small unit test for the extension. Note that this method is called in your setup section, not your assertion section.

[TestFixture]
public class MockExtensionsTest
{
  [TestCase]
  {
    // Setup
    var mock = new Mock<IAmAnInterface>();
    mock.ExpectsInOrder(
      x => x.MyMethod("1"),
      x => x.MyMethod("2"));

    // Fake the object being called in order
    mock.Object.MyMethod("1");
    mock.Object.MyMethod("2");
  }

  [TestCase]
  {
    // Setup
    var mock = new Mock<IAmAnInterface>();
    mock.ExpectsInOrder(
      x => x.MyMethod("1"),
      x => x.MyMethod("2"));

    // Fake the object being called out of order
    Assert.Throws<AssertionException>(() => mock.Object.MyMethod("2"));
  }
}

public interface IAmAnInterface
{
  void MyMethod(string param);
}