JustMock - How to mock a method for all instances by returning the result of the equivalent method of another class (sharing a common interface

Question

I am working with .NET 4.5, EF6 and I'm trying to use JustMock 2.0 to test my application.

I am trying to mock my database by mocking my DbContext subclass: CoreDataRepositoryContext.

To do it, I need to mock the member SaveChanges of DbContext and every DbSet typed properties of my class CoreDataRepositoryContext by returning a fake data collection. I also need to mock the following DbSet's members:

• Add
• Remove
• AsQueryable

I need to mock it for all instances of CoreDataRepositoryContext and DbSet

For example, I have entities of type Order in database (table Orders) I did the following to mock the table Orders:

// FakeOrders is a list of orders (List<Order>)

var mockedContext = Mock.Create<CoreDataRepositoryContext>();

   // Mock works
Mock.Arrange(() => mockedContext.SaveChanges()).IgnoreInstance().DoNothing();
   // Mock works
Mock.Arrange(() => mockedContext.Orders).IgnoreInstance().ReturnsCollection(FakeOrders);
   // Mock works
Mock.Arrange(() => mockedContext.Orders.Add(Arg.IsAny<Order>())).IgnoreInstance().DoInstead((Order o) => FakeOrders.Add(o));
   // Mock works
Mock.Arrange(() => mockedContext.Orders.Remove(Arg.IsAny<Order>())).IgnoreInstance().DoInstead((Order o) => FakeOrders.Remove(o));
   // Mock DOES NOT work !
Mock.Arrange(() => mockedContext.Orders.AsQueryable()).IgnoreInstance().Returns(() => FakeOrders.AsQueryable());

mockedContext.Orders is of type DbSet< Order > and FakeOrders is of type List< Order >. Both classes implement the interface IEnumerable< Order >.

Mocking Add and Remove members work well because neither of the two methods is declared in the interface IEnumerable< T >.

On the other hand, AsQueryable is declared in this interface and defined by Queryable. So, as I mock the member using IgnoreInstance, calling AsQueryable from an instance of any class which implements IEnumerable< T > launches a never ending loop. Because IEnumerable< Order >.AsQueryable is mocked by FakeOrders.AsQueryable which is mocked by... FakeOrders.AsQueryable... infinite loop...

var query = mockedContext.Orders.AsQueryable(); // Infinite loop
query = FakeOrders.AsQueryable(); // Infinite loop
query = new List<Order>().AsQueryable(); // Infinite loop

How can I do to only mock DbSet< Order >.AsQueryable specifically, without mocking IEnumerable< Order >.AsQueryable using IgnoreInstance?

Thank you for your help :)

Answer 1

Ok I have finally found a workaround:

I don't arrange DbContext with IgnoreInstance but I arrange the constructor of my DbContext subclass when called with a specific connection string as argument:

string myConnectionString = "CoreDBTestConnection";

// Arrange all CoreDataRepositoryContext instances for this connection string
Mock.Arrange(() => new CoreDataRepositoryContext(myConnectionString).Returns(GetMockContext());

The constructor is replaced by GetMockContext() which retruns a mocked context:

private static CoreDataRepositoryContext GetMockContext()
{
        CoreDataRepositoryContext mockContext = new CoreDataRepositoryContext();

        Mock.Arrange(() => mockContext.SaveChanges()).DoNothing();

        Mock.Arrange(() => mockContext.Set<Order>()).ReturnsCollection(FakeOrders);
        Mock.Arrange(() => mockContext.Orders).ReturnsCollection(FakeOrders);
        Mock.Arrange(() => mockContext.Orders.Add(Arg.IsAny<Order>())).DoInstead((Order o) => FakeOrders.Add(o));
        Mock.Arrange(() => mockContext.Orders.Remove(Arg.IsAny<Order>())).DoInstead((Order o) => FakeOrders.Remove(o));
        Mock.Arrange(() => mockContext.Orders.Find(Arg.IsAny<object[]>())).Returns((object[] param) => FakeOrders.Find(x => x.Id == (Guid)param[0]));
        Mock.Arrange(() => mockContext.Orders.AsQueryable()).Returns(() => FakeOrders.AsQueryable());

        // Then arrange all DbSets...

        return mockContext;
}

public static FakeDataList<Order> FakeOrders = new List<Order>();