JUnit not null test

Question

I'm trying to implement an easy junit test for a method. My intention is to test if the method parameter is not null. So that the test fails if the parameter is null.

the method is:

/*
 * @return the db entry object
*/
getEntry( String user, String grp, int status);

My first try to implement the test is

public void testGetEntry() {
    String userId = null;
    getEntry( userId, "grp1", 3);
    asserNotNull(userId);
}

I think thats not the correct way. thx for any help :)

Surely you need your *test* to validate that the method behaves correctly if the parameter *is* null - for example, checking that an exception is thrown. So, what *do* you want the method to do when the parameter is null? The check for that can't be in the test - it has to be in the production method. — Jon Skeet, May 17 '13 at 11:36
In your example, `userId` will *always* be null on the assert line, regardless of what `getEntry` does. — assylias, May 17 '13 at 11:38
I do not know if you really understand yourself what you try to accomplish, definetly we can not. Try to rethink what you try to do and explain it clearly — LionC, May 17 '13 at 11:40

score 3 · Answer 1 · answered May 17 '13 at 11:42

3

You can't test that. You can test a beavhior like : "Check that a IllegalArgumentException is thrown if a null parameter is passed". A unit test for testing if a parameter is not null does not make sense, it is not the purpose of unit testing : https://en.wikipedia.org/wiki/Unit_testing

Here, "test if the method parameter is not null" should be done in the method.

answered May 17 '13 at 11:42

Julien Bodin

783
3
19

Ok. i have to catch a possible NullPointerEx with the test. Am I right? – vicR May 17 '13 at 12:09
Do not play with fire, what will you do if you catch a NullPointerException ?If you don't want a null parameter for your method then check them first and throw yourself a IllegalArgumentException. – Julien Bodin May 17 '13 at 12:28

score 3 · Answer 2 · answered Jun 04 '13 at 16:00

You should definitely check out NullPointerTester from Guava. You use it in your tests like this:

new NullPointerTester().testAllPublicInstanceMethods(YourClass.class)

Then you need to annotate your methods with JSR-305s @NonNull

getEntry(@NonNull String user, @NonNull String grp, int status);

Then use Preconditions checkNotNull in your production code.

getEntry(@NonNull String user, @NonNull String grp, int status)
{
     Preconditions.checkNotNull(user, "user must be specified");
     Preconditions.checkNotNull(grp, "grp must be specified");
     //return entry;
}

This will make other classes receive a NullPointerException when they misuse your class. When they receive this they'll know that they did something wrong.

score 0 · Answer 3 · edited Jan 18 '18 at 08:49

In order to check that your method doesn't have a null parameter, you need to use Mockito and mock the class( let's call it C.java) where this method ( let's call it m(param) ) is declared. Of course class C should NOT be the class you want to test (a mock is a "dummy" implementation).

If you are in the case where you are calling the method m of class C and you want to verify that the argument "param" of m(param) is not null, here is how to do it :

C cMock= Mockito.mock(C.class);
verify(cMock).m(isNotNull());

Here is some useful documentation :

http://mockito.googlecode.com/svn/branches/1.6/javadoc/org/mockito/Matchers.html

http://mockito.googlecode.com/svn/branches/1.5/javadoc/org/mockito/Mockito.html

I hope this helps

Regards

JUnit not null test

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