DbSet mock, no results while calling ToList secondly

Question

I\'m trying to mock DbContext and DbSet. This works for my previous unit tests, but problem occurs while my code was calling ToList method on DbSet second time.

Firs

Answer 1

I just wanted to added to Wiktor Zychla's answer my little part. If someone is looking for Async version of this mock (coming from this tutorial: http://msdn.microsoft.com/en-us/data/dn314429.aspx#async) then this is my modification to TestDbAsyncEnumerator<T> class:

internal class TestDbAsyncEnumerator<T> : IDbAsyncEnumerator<T>
{
    private readonly IEnumerator<T> _inner;

    public TestDbAsyncEnumerator(IEnumerator<T> inner)
    {
        _inner = inner;
    }

    public TestDbAsyncEnumerator(Func<IEnumerator<T>> valueFunction)
    {
        _inner = valueFunction();
    }

    public void Dispose()
    {
        _inner.Dispose();
    }

    public Task<bool> MoveNextAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(_inner.MoveNext());
    }

    public T Current
    {
        get { return _inner.Current; }
    }

    object IDbAsyncEnumerator.Current
    {
        get { return Current; }
    }
}

Then like Wiktor suggested you have to setup it with delegate so in case of async it would be like that:

mockSet.As<IDbAsyncEnumerable<Blog>>()
            .Setup(m => m.GetAsyncEnumerator())
            .Returns(new TestDbAsyncEnumerator<Blog>(() => data.GetEnumerator()));

If someone wants source for that then here you go: https://github.com/kelostrada/EntityFrameworkWithMock.Test

Answer 2

I can't comment on Wiktor's post as I haven't got enough reputation, but i would like to add a little extra to Wiktor's answer.

The code

mockSet.Setup((m => m.GetEnumerator()).Returns(() => data.GetEnumerator())

Will fail if you give it a zero argument lambda like in the example(At least the version I am using). Passing an argument that is never used will allow it to meet the signature requirement however.

mockSet.Setup((m => m.GetEnumerator()).Returns(x => data.GetEnumerator())

Will compile however, and works as expected.

And this also applies to Kelu's answer as well (Although he has added the lambda in the wrong place.

mockSet.As<IDbAsyncEnumerable<Blog>>()
        .Setup(m => m.GetAsyncEnumerator())
        .Returns(x => new TestDbAsyncEnumerator<Blog>(data.GetEnumerator()));

Not trying to nitpick answers here, i'm just adding because i made these mistakes myself :)

Answer 3

You return the very same enumerator instance upon each call to GetEnumerator. When it enumerates once, it is done, EF doesn't call its Reset method, rather it asks for a new enumerator.

But you return the one that just has yielded all elements and yields no more.

Instead, return a function that returns the enumerator, that will return a new enumerator each time you ask for it.

 q.Setup(m => m.GetEnumerator()).Returns( () => queryableData.GetEnumerator() );

Answer 4

If you put a "Where" clause before the .ToList() call, the data should remain present.

var a1 = dbset.Where(m => m != null).ToList();

var a2 = dbset.Where(m => m != null).ToList();