Testing Exceptions using Java Reflection Junit4

Question

I have a function which returns an exception and i am writing a unit test case for it in Junit4. The issue is, reflect.invoke always wraps the exception in InvocationTargetException and hence unable to check the exception using ExpectedException class.

public class Hello {
private void printHello(String msg) {
    if ("hello".equals(msg)) {
        System.out.println("Hello");
    }
        else throw new HeaderException();
    }
}

Test:

@Rule
public ExpectedException expectedEx = ExpectedException.none();
@Test
public void testPrint() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    expectedEx.expect(HeaderException.class);

    Method method = Hello.class.getDeclaredMethod("printHello", String.class);
    method.setAccessible(true);
    method.invoke(Hello.class,"random");

}

Output:

    java.lang.AssertionError: 
Expected: an instance of com.locationguru.CSF.exception.HeaderException
     got: <java.lang.reflect.InvocationTargetException>
 <Click to see difference>

    at org.junit.Assert.assertThat(Assert.java:780)
    at org.junit.Assert.assertThat(Assert.java:738)
    at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:114)
    at org.junit.rules.RunRules.evaluate(RunRules.java:18)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
    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 sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

Possible duplicate of http://stackoverflow.com/questions/871216/junit-possible-to-expect-a-wrapped-exception — Marvin, Apr 21 '15 at 13:20
I would strongly discourage testing a private method like this. If you need it to be visible but not *too* visible, consider making it package-private. — Makoto, Apr 21 '15 at 17:09
At first I thought that `expectedEx.expectCause(instanceOf(HeaderException.class));` would do it but unfortunately the HeaderException is not stored in `cause` but in `target`. I suggest you write your own Matcher or search the web for a generic ExceptionMatcher. — CoronA, Apr 22 '15 at 06:59

score 7 · Accepted Answer · answered Apr 22 '15 at 06:43

7

One way of doing it could be to throw again the expected error , but is it recommended

 try
    {
        method.invoke(Hello.class, "random");
    }
    catch (InvocationTargetException e)
    {
        throw e.getTargetException();
    }

answered Apr 22 '15 at 06:43

shardy

357
2
6

Testing Exceptions using Java Reflection Junit4

1 Answers1