Question

Let’s say I have a bunch of classes that look something like…

class Foo{
  private Bar highlyCoupled = new highlyCoupled();

  public bool DoTheThing(){
    return highlyCoupled.doesTheThing();
  } 
}

Is it possible to use reflection to open up foo and inject (duck-punch may be a more correct term) some sort of mockHighlyCoupled in the place of highlyCoupled?

What about in this situation…

class DoubleFoo : Foo{
  public bool DoTheOtherThing(){
    return DoTheThing();
  }
}

Can the inherited highlyCoupled have a mock inserted in it’s place?

Refactoring the code so as to not require reflection isn’t possible, unfortunately.

Answer 1

Since you can’t refactor using a mocking framework could make this a bit easier for you. For Example:

TypeMock:

var fakeType = Isolate.Fake.Instance<SomeType>();
ObjectState.SetField(fakeType, "_somePrivateField", myValue);

Moq:

var fakeType = new Mock<SomeType>()
fakeType.Protected().Setup<SomeType>("_somePrivateField").Returns(myValue);

To be honest I haven’t actually tried this out with Moq but I think it will do what you need.