Getting arguments passed to a FakeItEasy-mock without using magic strings?

Question

I have been using Moq for my mocking needs the last years, but after looking at FakeItEasy i wanted to give it a try.

I often want to test that a method have been called with the correct parameters, but i found no satisfactory way to do this with FakeItEasy.

I have the following code to test:

    public class WizardStateEngine : IWizardStateEngine
{
    private readonly IWorkflowInvoker _workflowInvoker;
    private List<CustomBookmark> _history;

    public WizardStateEngine(IWorkflowInvoker workflowInvoker)
    {
        _workflowInvoker = workflowInvoker;
    }

    public void Initialize(List<CustomBookmark> history)
    {
        _history = history;
    }

    public WizardStateContext Execute(Command command, WizardStateContext stateContext, CustomBookmark step)
    {
        Activity workflow = new MyActivity();
        var input = new Dictionary<string, object>();
        input["Action"] = command;
        input["Context"] = stateContext;
        input["BookmarkHistory"] = _history;

        var output = _workflowInvoker.Invoke(workflow, input);

        _history = output["BookmarkHistory"] as List<CustomBookmark>;

        return output["Context"] as WizardStateContext;
    }

    public List<CustomBookmark> GetBookmarkHistory()
    {
        return _history;
    }
}

I want to write some tests that verifies the input to _workflowInvoker.Invoke(). My TestInitialize method sets up the needed resources and save the input dictionary to _workflowInvoker.Invoke() as a local field _wfInput.

    [TestInitialize]
    public void TestInitialize()
    {
        _wizardStateContext = new WizardStateContext();
        _workflowInvoker = A.Fake<IWorkflowInvoker>();
        _wizardStateEngine = new WizardStateEngine(_workflowInvoker);

        _outputContext = new WizardStateContext();
        _outputHistory = new List<CustomBookmark>();
        _wfOutput = new Dictionary<string, object>
                        {{"Context", _outputContext}, {"BookmarkHistory", _outputHistory}};

        _history = new List<CustomBookmark>();

        A.CallTo(() =>
                 _workflowInvoker.Invoke(A<Activity>.Ignored, A<Dictionary<string, object>>.Ignored))
            .Invokes(x => _wfInput = x.Arguments.Get<Dictionary<string, object>>("input"))
            .Returns(_wfOutput);

        _wizardStateEngine.Initialize(_history);
    }

After the setup i have multiple tests like this:

    [TestMethod]
    public void Should_invoke_with_correct_command()
    {
        _wizardStateEngine.Execute(Command.Start, null, null);

        ((Command) _wfInput["Action"]).ShouldEqual(Command.Start);
    }

    [TestMethod]
    public void Should_invoke_with_correct_context()
    {
        _wizardStateEngine.Execute(Command.Start, _wizardStateContext, null);

        ((WizardStateContext) _wfInput["Context"]).ShouldEqual(_wizardStateContext);
    }

    [TestMethod]
    public void Should_invoke_with_correct_history()
    {
        _wizardStateEngine.Execute(Command.Start, _wizardStateContext, null);

        ((List<CustomBookmark>) _wfInput["BookmarkHistory"]).ShouldEqual(_history);
    }

I do not like the magic string "input" in the TestInitialize for getting the passed argument (or magic number). I can write the tests without the local field like this:

    [TestMethod]
    public void Should_invoke_with_correct_context()
    {
        _wizardStateEngine.Execute(Command.Start, _wizardStateContext, null);

        A.CallTo(() =>
                 _workflowInvoker.Invoke(A<Activity>._,
                                         A<Dictionary<string, object>>.That.Matches(
                                             x => (WizardStateContext) x["Context"] == _wizardStateContext)))
            .MustHaveHappened();
    }

But i find the tests with the local field more readable.

Are there any way to setup saving of the input as a field i my test class without magic numbers or strings?

I hope the updated example in the question shows why i would like to use the local field. I am more than willing to write my tests without the local field if i can find a nice readable way to do it.

Answer 1

A.CallTo(() => service.DoSomething(A<int>.That.Matches(x => x == 100)))
 .MustHaveHappened();