Entity Framework extension methods in unit test using Moq and Autofac
I am mocking DbSet from Entify Framework. I want to use his extension method ToListAsync
. This is how I do it and below is the result of my attempt (normal ToList
works):
IQueryable<DbUser> userData = MockedData.Instance.Users; // this is just a property to get custom IQueryable set of data for testing
var dbSetMock = new Mock<DbSet<DbUser>>();
dbSetMock.As<IQueryable<DbUser>>().Setup(m => m.Provider).Returns(userData.Provider);
dbSetMock.As<IQueryable<DbUser>>().Setup(m => m.Expression).Returns(userData.Expression);
dbSetMock.As<IQueryable<DbUser>>().Setup(m => m.ElementType).Returns(userData.ElementType);
dbSetMock.As<IQueryable<DbUser>>().Setup(m => m.GetEnumerator()).Returns(userData.GetEnumerator());
/*
I've put it here so you can see how I tried to approach my problem
dbSetMock.Setup(x => x.ToListAsync())
.Returns(Task.FromResult(userData.ToList()));
*/
var testAsync = dbSetMock.Object.ToListAsync();
var testRegular = dbSetMock.Object.ToList();
Results:
The variable testRegular
matters as expected. But the variable testAsync
has a value like this:
When I uncomment the part where I am trying to set ToListAsync
in order to return anything, I get an exception like this:
{"Expression references a method that does not belong to the mocked object: x => x.ToListAsync<DbUser>()"}
Any suggestions would be appreciated. Should I switch to fakes? is this functionality supported?
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I found and used this code with success:
dbSetMock.As<IDbAsyncEnumerable<DbUser>>()
.Setup(m => m.GetAsyncEnumerator())
.Returns(new AsyncEnumerator<DbUser>(userData.GetEnumerator()));
with the following support class (note the use of C # 6 shorthand functions):
class AsyncEnumerator<T> : IDbAsyncEnumerator<T>
{
private readonly IEnumerator<T> _inner;
public AsyncEnumerator(IEnumerator<T> inner)
{
_inner = inner;
}
public void Dispose() => _inner.Dispose();
public Task<bool> MoveNextAsync(CancellationToken cancellationToken) => Task.FromResult(_inner.MoveNext());
public T Current => _inner.Current;
object IDbAsyncEnumerator.Current => Current;
}
The main reason for the error is that Moq cannot mimic static methods, at least for now.
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