Mock an enum using Mockito in Java

Question

How can I mock an enum for testing purposes using Mockito? Given this sample for the enum:

public enum TestEnum {
 YES,
 NO
}

and this one for the method using the enum:

public static boolean WorkTheEnum(TestEnum theEnum) {
switch (theEnum) {
  case YES:
     return true;
  case NO:
     return false;
  default:
     // throws an exception here
 }
}

how can I mock the enum to reach the default branch of the switch loop? This answer says Mockito can't mock enums but the answer has also been provided more than a year ago. Do I can mock an enum meanwhile or have I to let the branch stay untested? Other Mocking frameworks can't be used.

Solution

There are two answers to that:

a) you could turn to some PowerMock-like mocking framework. My two cent(entences) there: don't do that. PowerMock opens a door to the land of pain; which you do not want to enter.

b) put interfaces on your enums

Seriously; I nowadays think that there is only one good use case for enums; and that is to use them as singletons that provide a certain service. And then, I do this:

public interface FooService { void foo(); }
class FooServiceImpl implements FooService { @Override void foo() ...
enum FooServiceProvider implements FooService {
   INSTANCE;
   private final FooService impl  = new FooServiceImpl();
   @Override foo() { impl.foo()

Of course, this doesn't really help when you use enums like you do. But the thing is: you shouldn't be using enums that way anyway. Because using enums this way leads to shattered code - every place that takes an enum variable is in need for such switch statements; with all the negative consequences when you add / remove enum cases.

So, in your case: consider turning to true OO designs - where you have abstract base classes that define methods; and then you use factories to create subclasses (probably based on enum switches) that give you objects that simply do the right thing.

Comments

[J.Mengelle]

Enum are like static class therefore you can't moke them with mokito.In your sample, the default is unreachable, so you can't test it.