Mocking classes that implement IQueryable with Moq

c# unit-testing mocking moq
LeffeBrune picture LeffeBrune · Aug 13, 2011 · Viewed 17.4k times · Source

I spent an evening trying to mock an object that implements IQueryable:

public interface IRepo<T> : IQueryable<T>
{
}

The best I could come up with is something like this:

var items = new Item[] {}.AsQueryable();

var repo = new Mock<IRepo>();
repo.Setup(r => r.GetEnumerator()).Returns(items.GetEnumerator());
repo.Setup(r => r.Provider).Returns(items.Provider);
repo.Setup(r => r.ElementType).Returns(items.ElementType);
repo.Setup(r => r.Expression).Returns(items.Expression);

Is there a more concise way to do the same? It would be easier to expose a property/method in IRepo that returns IQueryable and the simply mock like this:

repo.Setup(r => r.GetItems()).Returns(new Items[]{ }.AsQueryable());

But this is not what I want to do =)

Answer

Rune Jacobsen picture Rune Jacobsen · Dec 16, 2011

This is nothing new, just a cleaner way of doing it. I also have repositories where the repository itself is also an IQueryable, so I needed the same thing. I basically just put your code into an extension method like this at the root level of my test project, to make it available to all tests:

public static class MockExtensions
{
    public static void SetupIQueryable<T>(this Mock<T> mock, IQueryable queryable)
        where T: class, IQueryable
    {
        mock.Setup(r => r.GetEnumerator()).Returns(queryable.GetEnumerator());
        mock.Setup(r => r.Provider).Returns(queryable.Provider);
        mock.Setup(r => r.ElementType).Returns(queryable.ElementType);
        mock.Setup(r => r.Expression).Returns(queryable.Expression);
    }
}

This basically just offers reusability, since you're likely to want to do this in several tests, and in each test it makes the intention clear and the mess minimal. :)

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