Intercepting JUnit Assert functions

Question

I would like to do some "own stuff" when an assertion in JUnit fails. I would like to have this:

public class MyAssert extends org.junit.Assert {

    // @Override
    static public void fail(String message) {
        System.err.println("I am intercepting here!");
        org.junit.Assert.fail(message);
    }
}

Of course, this does not work, because you cannot override static methods. But if it would, this would be nice, because every assert function like assertTrue() calls the fail() method. Thus, I could easily intercept every assertion.

Does there exist any way to do what I want to do here, without implementing all different flavors of assert...?

Answer 1

You should take a look at the Rules, that were introduced in Junit 4.7. Especially TestWatchman:

TestWatchman is a base class for Rules that take note of the testing action, without modifying it. For example, this class will keep a log of each passing and failing test:

http://junit-team.github.io/junit/javadoc/4.10/org/junit/rules/TestWatchman.html

It lets you define a MethodRule that can handle failing Tests (Copy from the javadoc):

   @Rule
    public MethodRule watchman= new TestWatchman() {
            @Override
            public void failed(Throwable e, FrameworkMethod method) {
                    watchedLog+= method.getName() + " " + e.getClass().getSimpleName()
                                    + "\n";
            }

            @Override
            public void succeeded(FrameworkMethod method) {
                    watchedLog+= method.getName() + " " + "success!\n";
            }
    };

    @Test
    public void fails() {
            fail();
    }

    @Test
    public void succeeds() {
    }

As per comment TestWatchman is depecreated in newer Versions of Junit and replaced with TestWatcher (but the functionality is the same):

http://junit-team.github.io/junit/javadoc/4.10/org/junit/rules/TestWatcher.html

Answer 2

You could write a class that implements exactly the same signatures of all the methods in Assert and then delegates to the Assert methods.

public class MyAssert {
    static public void assertTrue(String message, boolean condition) {
        Assert.assertTrue(message, condition);
    }

    ...

    static public void fail(String message) {
        System.err.println("I am intercepting here!");
        Assert.fail(message);
    }
}

Not exactly re-implementing all the methods, but tedious nonetheless. Your IDE may be able to help in generating the delegate methods.