Why does Fakes execute real method?

Question

I've stubbed a class using MS Fakes. This class is injected into another class that is not stubbed:

var stubClassA = new MyNamespace.Fakes.StubClassA();
ClassB classB = new ClassB(stubClassA);
classB.DoSomething(10);

When I step into classB.DoSomething(), the classA instance is there and I can see it is correctly stubbed.

In classB.DoSomething(int empId)

classA.GetEmployee(empId);

The above does a real call to classA.GetEmployee(). Shouldn't that just return null and not try to execute the real code?

I did try to stub GetEmployee():

stubClassA.GetEmployee = (value) => new Employee();

but it throws the compile time error:

Cannot assign to 'GetEmployee' because it is a 'method group'

Signature of GetEmployee in ClassA

public Employee GetEmployee(int empId)

Any ideas what I'm doing wrong?

Answer 1

You need to ensure that your ClassA implements an interface, so that MS Fakes can implement a stub for it.

A small example that I threw together:

namespace TestLib
{
    public class Employee
    {
        public int Id;
    }

    public interface IClassA
    {
        Employee GetEmployee(int empId);
    }
    public class ClassA : IClassA
    {
        public Employee GetEmployee(int empId)
        {
            return new Employee(){Id = empId};
        }
    }

    public class ClassB
    {
        private IClassA _classA;

        public ClassB(IClassA a)
        {
            this._classA = a;
        }

        public void DoSomething(int id)
        {
            _classA.GetEmployee(id);
        }
    }
}

Now you can stub out ClassA like so:

var b = new StubIClassA()
{
    GetEmployeeInt32 = (val) => new StubEmployee()
};