Unit Test SqlFunctions

Question

I have a repository that exposes IQueryable and a service handles specific queries and here a few methods that make use of DbFunctions. In order to be testable, i create a fake repository with static list of elements and inject it into the service. Problem is, since my service queries a List and does not make use of database, i get the error "This function can only be invoked from LINQ to Entities.".

Is there any easier way for testing this than creating a fake DbFunctions and QueryProvider?

Thanks in advance

Answer 1

I'm tried to implement dateDiff function, and it's works for me but we should think that in that case we test different functions and we are testing not real behaviour

 private class MySqlFunctions
    {
        [DbFunction("SqlServer", "DATEDIFF")]//EF will use this function
        public int? DateDiff(string datePartArg, DateTime startDate, DateTime endDate)
        {
            var subtract = startDate.Subtract(endDate);
            switch (datePartArg)
            {
                case "d":
                    return (int?)subtract.TotalDays;
                case "s":
                    return (int?)subtract.TotalSeconds; // unit test will use this one
            }
            throw new NotSupportedException("Method supports only s or d param");
        }
    }

Then in linq code

var sqlFunctions = new MySqlFunctions();

var result = matches.Average(s => sqlFunctions.DateDiff("s", s.MatchCreated, s.WaitingStarted);