How to assert an IEnumerable parameter where order is unimportant?

Question

I'm writing a unit test, I want to ensure that a particular method is called with some parameters:

var myMock = MockRepository.GenerateMock<IMyService>();

IMyService has a method on it with the signature

public bool SomeMethod(IEnumerable<string> values)

I have a business logic layer which consumes my mock

public class BusinessLogic
{
  protected MyMock MyMock{get;set;}

  public BusinessLogic (myMock)
  {
    this.MyMock = myMock;
  }

  public bool DoLogic()
  {
    var myCollection = // loaded from somewhere
    return this.MyMock(myCollection);
  }
}

I want to test the DoLogic method by making sure that it calls SomeMethod properly. However I have no control (and don't really want it over the ordering of the collection).

I want to assert that the method SomeMethod is called with the IEnumerable {"a", "b", "c"} but I don't care on the order.

So far I have

myMock.Expect(x => x.MyMethod(new string[]{"a", "b", "c"});

and

myMock.AssertWasCalled(x => x.MyMethod(new string[]{"a", "b", "c"});

But this will fail if it's called with {"b", "a", "c"}. I don't want to change my business logic to ensure the ordering of the parameters (as this would design the BLL around the tests).

How can I assert this method call?

Answer 1

You can use Arg<T>.Matches:

myMock.Expect(x => x.MyMethod(Arg<IEnumerable<string>>.Matches(s => !s.Except(expected).Any() && !expected.Except(s).Any()));

Answer 2

Test frameworks usually have assertions for such matching, you can mix those two. Example with NUnit's EquivalentTo:

myMock.Expect(x => x.MyMethod(Arg<IEnumerable<string>>.Matches(value => 
{
    Assert.That(value, Is.EquivalentTo(new[] { "c", "b", "a" }));
    return true;
}));

This way, produced error message should be more descriptive than what Rhino will generate.