TestDbAsyncQueryProvider fixed to use with AutoMapper's ProjectTo

TestDbAsyncQueryProvider.cs

// TestDbAsyncQueryProvider from https://msdn.microsoft.com/en-us/library/dn314429(v=vs.113).aspx

internal class TestDbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider
{
    private readonly IQueryProvider _inner;

    internal TestDbAsyncQueryProvider(IQueryProvider inner)
    {
        _inner = inner;
    }

    public IQueryable CreateQuery(Expression expression)
    {
        switch (expression)
        {
            case MethodCallExpression m:
                {
                    var resultType = m.Method.ReturnType; // it shoud be IQueryable<T>
                    var tElement = resultType.GetGenericArguments()[0];
                    var queryType = typeof(TestDbAsyncEnumerable<>).MakeGenericType(tElement);
                    return (IQueryable)Activator.CreateInstance(queryType, expression);
                }
        }
        return new TestDbAsyncEnumerable<TEntity>(expression);
    }

    public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
    {
        return new TestDbAsyncEnumerable<TElement>(expression);
    }

    public object Execute(Expression expression)
    {
        return _inner.Execute(expression);
    }

    public TResult Execute<TResult>(Expression expression)
    {
        return _inner.Execute<TResult>(expression);
    }

    public Task<object> ExecuteAsync(Expression expression, CancellationToken cancellationToken)
    {
        return Task.FromResult(Execute(expression));
    }

    public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken)
    {
        return Task.FromResult(Execute<TResult>(expression));
    }
}