Unit testing with queries defined in extension methods

Question

In my project I am using the following approach to querying data from the database:

1. Use a generic repository that can return any type and is not bound to one t

Answer 1

To isolate testing just to just the extension method i wouldn't mock anything. Create a list of Invoices in a List() with predefined values for each of the 3 tests and then invoke the extension method on the fakeInvoiceList.AsQueryable() and test the results.

Create entities in memory in a fakeList.

var testList = new List<Invoice>();
testList.Add(new Invoice {...});

var result = testList().AsQueryable().ByInvoiceType(enumValue).ToList();

// test results

Answer 2

If it suits your conditions, you can hijack generics to overload extension methods. Lets take the following example:

interface ISession
{
    // session members
}

class FakeSession : ISession
{
    public void Query()
    {
        Console.WriteLine("fake implementation");
    }
}

static class ISessionExtensions
{
    public static void Query(this ISession test)
    {
        Console.WriteLine("real implementation");
    }
}

static void Stub1(ISession test)
{
    test.Query(); // calls the real method
}

static void Stub2<TTest>(TTest test) where TTest : FakeSession
{
    test.Query(); // calls the fake method
}