Mocking classes that implement IQueryable with Moq

问题:

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 =)

回答1:

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. :)

回答2:

Rune's answer is awesome and saved me time figuring out how to do the same. Small gotcha is that if you call some IQueryable extension methods on your IQueryable twice (e.g. ToList()) then the second time you'll get no results back. That's because the enumerator is at the end and needs resetting. Using Rhinomocks I changed the implementation for GetEnumerator to:

mock.Stub(r => r.GetEnumerator()).Do((Func<IEnumerator<T>>) (() => { 
    var enumerator = queryable.GetEnumerator();
    enumerator.Reset();
    return enumerator;
}));

Hope that saves someone some time.

回答3:

I like Rune's answer. Here's a generic IQueryable version:

public static void SetupIQueryable<TRepository, TEntity>(this Mock<TRepository> mock, IQueryable<TEntity> queryable)
   where TRepository : class, IQueryable<TEntity>
{
    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);
}

回答4:

I think that's about the best you can do with Moq. I think a more readable option would be to roll your own FakeRepo<T> that derives from System.Linq.EnumerableQuery<T>:

public class FakeRepo<T> : EnumerableQuery<T>, IRepo<T>
{
    public FakeRepo(IEnumerable<T> items) : base(items) { }
}

Update: You might be able to pull this off by mocking EnumerableQuery<T> then using As<T>():

var items = new Item[0];

var repo = new Mock<EnumerableQuery<Item>(items).As<IRepo>();

回答5:

I had the same issue. I've fixed it by changing this line

mock.Setup(r => r.GetEnumerator()).Returns(queryable.GetEnumerator());

to

mock.Setup(r => r.GetEnumerator()).Returns(queryable.GetEnumerator);

I hope that additional comments are not required here.