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Powermock - null is returned

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I need your help with the following issue related with Junit testing:

I have the following class under test:

and the following unit test

when I uncomment the  "assertEquals("res",ExceptionUtil.stackToString(throwMock));" code I'm getting a null object returned.

java.lang.AssertionError: expected:<res> but was:<null>
at org.junit.Assert.fail(Assert.java:88)
at org.junit.Assert.failNotEquals(Assert.java:834)
at org.junit.Assert.assertEquals(Assert.java:118)
at org.junit.Assert.assertEquals(Assert.java:144)
at com.vw.client.test.ExceptionUtilTest.test(ExceptionUtilTest.java:44)

I've tried to debug the method under test with Junit but without any success.

What I'm doing wrong?


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I'm confused... what are you trying to test here?  Because line 31 mocks all the static methods of the ExceptionUtil class and yet the rest of the test code appears to be wanting to test the static stackToString() method.

You don't mock code that you're actually trying to test. You only mock the dependencies that you want to control the behavior of. The Throwable object that the stackToString() method is collaborating with can be mocked but not the method under test itself.

This is the problem with mocks, especially when you're just starting out with unit testing. Beginners often get confused and end up testing mocks themselves instead of the production code.

The PowerMock README wrote:Please note that PowerMock is mainly intended for people with expert knowledge in unit testing. Putting it in the hands of junior developers may cause more harm than good.

If you're just trying to learn how to unit test, I suggest you start out by NOT using mock objects.
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