6

Lets say I have a method that looks like this:

public static String[] parseFoo(Foo anObject){
    Foo anotherObject = parseFoo2(anObject);
...
}

private static Foo parseFoo2(Foo anObject){
...
}

and both methods are in the same class. parseFoo2 is just a helper method that helps parseFoo get some stuff done. I'm trying to test the method parseFoo. Is there anyone in EasyMock that I can specify a return value on that private method call for parseFoo2 like the way I can specify instance method calls for an object with 

EasyMock.createMock(...);
anObject.expect(...).andReturn(...);

because I want to test the public method, but I don't want to have to go into the private method and test the implementation inside.

Thanks

KWJ2104
  • 1,959
  • 6
  • 38
  • 53

3 Answers3

13

Don't do it. One of the corner stones of a good unit test is that it should rely as little as possible on implementation details. Mocking out a private method is exactly that.

Why? Because that makes your unit tests very brittle. Consider the situation where you come back to this code in a week and decide that you don't really need the method parseFoo2 and you actually want to inline its code. Or that you want to split this method into two or more smaller methods. All very valid refactoring practices- but they will break the unit test!

You don't want to be chasing unit tests each time you make a simple refactoring like that. Hence, it is considered bad practice to mock private methods.

Ruan Mendes
  • 90,375
  • 31
  • 153
  • 217
Vitaliy
  • 8,044
  • 7
  • 38
  • 66
  • 2
    This answer is too absolutist, and it takes a philosophical veiw point that private methods don't have an internal contract that should be tesed. If the method is used in several places in the class, it's just like a public method in that it needs to maintain it's behavior pattern. Also if you have a method that calls several methods (all private) each with 2-3 logic paths testing the top level method becomes very complex. Nothing is worse than a complex test that is failing when you need to check in :). I much prefer a frequent predictable cost to an occasional roadblock. – Gus Aug 20 '12 at 15:08
  • 2
    @Gus, I do not agree. From a pragmatic perspective, testing private methods with high granularity would prevent you from easily refactoring your code. I would agree that as complexity grows, it should be factored to pieces that should be tested separately. Classes should be considered in this case. from a philosophic perspective, I would argue that a private section of a class is not a Unit that should be tested. It is an implementation detail, while tests should reflect the requirements from the object under test, not its inner workings. – Vitaliy Aug 20 '12 at 17:03
  • I would agree that is is sometimes you need to mock a private method- for example, in cases where the mocking of the internal (private) logic is very complex and misses the point of the test. But these cases are relatively rare and usually point to another design flow. Regardless, it does not fall on the use case of the OP. – Vitaliy Aug 20 '12 at 17:13
9

If you find that you must mock out a private method, then you can use PowerMock.expectPrivate(). EasyMock is not capable of mocking private methods.

Makoto
  • 104,088
  • 27
  • 192
  • 230
0

If you still want to use EasyMock, because changing it doesn't depend on you (work in an enterprise) you can use reflection to change the private field which your method returns, or any private field for that matter.

You can have these methods in a helper class for example. And use them as needed.

dalvarezmartinez1
  • 1,385
  • 1
  • 17
  • 26
  • Have you ever been able to get this to work? I've tried several times without luck so far. – HardcoreBro Jun 26 '13 at 13:45
  • In my case parseFoo2 was in another class but i needed to modify what it was returning, in the end a private static field of that class right?So.. public static void helpMethodForStaticFiled(Class> class, String fieldName, Object fieldValue) { Field field = class.getDeclaredField(fieldName); field.setAccessible(true); field.set(null, fieldValue); field.setAccessible(false); } And now if I have a private static MyField myField in class MyClass, i do something like: helpMethodForStaticFiled(MyClass.class, "myField", new MyField()); – dalvarezmartinez1 Jul 08 '13 at 08:22