使用jmockit，如何避免两种情况之间的影响？

Question

I have two classes, the first class:

public class FirstClass {
    private static final Logger LOG = Logger.getLogger(FirstClass.class);

    public void action(){
        LOG.info("FirstClass.action.");
    }
}

the second class:

public class SecondClass {
    private static final Logger LOG = Logger.getLogger(SecondClass.class);

    public void action(){
        FirstClass firstClass = new FirstClass();
        firstClass.action();
    }
}

I will write unit test for these two classes, the first class unit test:

public class FirstClassTest {
    @Test
    public void testAction(){
        FirstClass firstClass = new FirstClass();
        firstClass.action();
    }
}

the second class unit test:

public class SecondClassTest {
    @Mocked
    private Logger LOG;

    @Mocked
    private FirstClass firstClass;

    @Test
    public void testAction(){
        SecondClass secondClass = new SecondClass();
        secondClass.action();
    }
}  

About the second class unit test, As the second class depend on the first class, so I mocked the first class, at same time I also mocked Logger class.

I add a suite class to run these two classes:

@RunWith(Suite.class)
@Suite.SuiteClasses({SecondClassTest.class ,FirstClassTest.class})
public class TestAll {
}

When I run this suite class, it throw the follow exception:

java.lang.NullPointerException
at org.apache.log4j.Category.info(Category.java:663)
at steve.test.jmockit.issues.mocklog4j.FirstClass.action(FirstClass.java:12)
at steve.test.jmockit.issues.mocklog4j.FirstClassTest.testAction(FirstClassTest.java:12)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:78)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:212)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:68)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

From this trace log, the LOG of first class has been mocked. but in fact I don't mock Logger in FirstClassTest class.

But when I changed this suite class, firstly run FirstClassTest.class, and then run SecondClassTest.class. all cases are successful.

@RunWith(Suite.class)
@Suite.SuiteClasses({FirstClassTest.class ,SecondClassTest.class})
public class TestAll {
}

How to fix this issue and ensure that there is no effect between the two cases? Thanks!

Answer 1

The exception occurs because both tests call LOG.info(...) on the same LOG instance, with this being an uninitialized instance (ie, an instance with all of its reference fields null ).

The reason LOG holds an uninitialized instance is that the Logger class got mocked when the first test was executed. The class gets unmocked before the second test runs, but that doesn't change the state of the LOG object. So, when the second call to LOG.info(...) occurs, it is not mocked, but attempts to use Logger fields which are still null , causing the NPE.

The way to avoid the problem is to ensure the LOG field gets initialized before the Logger class is mocked. This can be done, for example, by adding a @BeforeClass method which instantiates FirstClass (since it holds the LOG field in question).

Answer 2

I ran the first Suite and do not see the issue you describe. My output is:

Jul 09, 2015 12:00:59 AM First action
INFO: FirstClass.action.

I'm using JMockit 1.18; JDK 1.8; JUnit 4.12