How to test enum types

Question

I m currently trying to build a more or less complete set of unit tests for a small library  Since we want to allow different implementations to exist we want this set of tests to be  a  generic  so that we can re-use it to test the different implementations and  b  as complete as possible  For the  b  part I d like to know if there is any best-practice out there for testing enum types  So for example I have an enum as follows   public enum Month       January      February              December      Here I want to ensure that all enum types really exist  Is that even necessary  Currently I m using Hamcrests assertThat like in the following example   assertThat Month January  is notNullValue        A missing  January  enum would result in a compile time error which one can fix by creation the missing enum type   I m using Java here but I don t mind if your answer is for a different language    Edit   As mkato and Mark Heath have both pointed out testing enums may not be necessary since the compiler won t compile when you are using an enum type which isn t there  But I still want to test those enums since we want to build a seperate TCK-like test jar which will run the same test on different implementations  So my question was more meant to be like  What is the best way to test enum types   After thinking about it a bit more I changed the Hamcrest statement above to   assertThat Month valueOf  January    is notNullValue        This statement now throws a NPE when January is not there  yet   Is there anything wrong with this approach

User · Answer

If you use all of the months in your code, your IDE won't let you compile, so I think you don't need unit testing.

But if you are using them with reflection, even if you delete one month, it will compile, so it's valid to put a unit test.

User · Answer

Usually I would say it is overkill  but there are occasionally reasons for writing unit tests for enums   Sometimes the values assigned to enumeration members must never change or the loading of legacy persisted data will fail  Similarly  apparently unused members must not be deleted  Unit tests can be used to guard against a developer making changes without realising the implications

User · Answer

you can test if have exactly some values  by example   for MyBoolean b   MyBoolean values          switch b        case TRUE          break      case FALSE          break      default          throw new IllegalArgumentException b toString        for String s   new String    TRUE    FALSE           MyBoolean valueOf s       If someone removes or adds a value  some of test fails

User · Answer

I agree with aberrant80      For enums  I test them only when they actually have methods in them    If it s a pure value-only enum like your example  I d say don t   bother       But since you re keen on testing it  going with your second option is   much better than the first  The problem with the first is that if you   use an IDE  any renaming on the enums would also rename the ones in   your test class    I would expand on it by adding that unit testings an Enum can be very useful  If you work in a large code base  build time starts to mount up and a unit test can be a faster way to verify functionality  tests only build their dependencies   Another really big advantage is that other developers cannot change the functionality of your code unintentionally  a huge problem with very large teams    And with all Test Driven Development  tests around an Enums Methods reduce the number of bugs in your code base   Simple Example  public enum Multiplier       DOUBLE 2 0       TRIPLE 3 0        private final double multiplier       Multiplier double multiplier            this multiplier   multiplier             Double applyMultiplier Double value            return multiplier   value            public class MultiplierTest         Test     public void should             assertThat Multiplier DOUBLE applyMultiplier 1 0   is 2 0            assertThat Multiplier TRIPLE applyMultiplier 1 0   is 3 0

User · Answer

For enums  I test them only when they actually have methods in them  If it s a pure value-only enum like your example  I d say don t bother   But since you re keen on testing it  going with your second option is much better than the first  The problem with the first is that if you use an IDE  any renaming on the enums would also rename the ones in your test class

[unit-testing] How to test enum types?

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