Am I missing something when trying to mock out a linq query?

[Lee Prosser]

So in the real world I have something which returns an IEnumerable then an Any query happens to it then some other logic occurs, but I was struggling to mock out the query.

Here is an example of me isolating the use case

[Test]

        public void dummy_test()

        {

            var mockEnumerable = Substitute.For<IEnumerable<int>>();

            mockEnumerable.Any(Arg.Any<Func<int, bool>>()).Returns(x => true);

            var res = mockEnumerable.Any(x => x == 10);

            Assert.That(res, Is.True);

        }

So I thought that would be fine, but it just blows up on the stubbing the any field with 

System.ArgumentNullException : Value cannot be null.


Parameter name: predicate

I have tried just doing .Any(x => true).ReturnsWithAnyArg(x => true); but that blows up too.

So is there a special way to mock out linq queries on an object?

[David Tchepak]

`Any` is an extension method on `IEnumerable<T>`. NSubstitute can't mock extension methods.

I don't think I ever substitute for `IEnumerable<T>`, I use real collections instead. For example:

    mySub.Widgets.Returns(new [] { new Widget(1), new Widget(2) });

If you can give a bit more info about the scenario you are trying to test I'm happy to try to come up with some ideas on how to test it.

Regards,

David

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