[Fact]
public void ShouldReturnEntity()
{
    var db = Mock.Create<MyModel.MyModel>();
    Mock.Arrange(() => db.SomeEntities).ReturnsCollection(someEntities);

    var entity = db.SomeEntities.SingleAsync(x => x.Id == 1);

    Assert.NotNull(entity);
}

The outcome is the the following exception:

System.InvalidOperationException
The provider for the source 'IQueryable' doesn't implement 'IAsyncQueryProvider'. Only providers that implement 'IAsyncQueryProvider' can be used for Entity Framework asynchronous operations.