Hard-Coded Mock Objects vs Mocking Framework

Question

I'm curious as to what method people like to use for mocking and why. The two methods that I know of are using hard coded mock objects and a mocking framework. To demonstrate, I'll outline an example using C#.

Suppose we have an IEmployeeRepository interface with a method called GetEmployeeById.

public interface IEmployeeRepository
{
    Employee GetEmployeeById(long id);
}

We can easily create a mock of this:

public class MockEmployeeRepository : IEmployeeRepository
{
    public Employee GetEmployeeById(long id)
    {
        Employee employee = new Employee();
        employee.FirstName = "First";
        employee.LastName = "Last";
        ...
        return employee;
    }
}

Then, in our tests we can explicitly tell our services to use the MockEmployeeRepository, either using a setter or dependency injection. I'm new to mocking frameworks so I'm curious as to why we use them, if we can just do the above?

Answer 1

A mocked interface can have different outputs per test - One test you may have a method return null, another test has the method return an object, another test has the method throw an exception. This is all configured in the unit test, whereas your version would require several hand-written objects.

Psuedocode:

//Unit Test One

MockObject.Expect(m => m.GetData()).Return(null);

//Unit Test Two

MockObject.Expect(m => m.GetData()).Return(new MyClass());

//Unit Test Three

MockObject.Expect(m => m.GetData()).ThrowException();