JUnit4 : Test a shutdown hook is called

Question

I have a method which adds a shutdown hook. I need to test (via JUnit) that the code executed in the hook is called :

public void myMethod(){
    Runtime.getRuntime().addShutdownHook(new Thread() {

        @Override
        public void run() {
            ... code to test ...
        }
    });
}

How can I simulate a shutdown in my unit test ?

Answer 1

I don't think you'll be able to test that. Instead, just test that your code behaves correctly when invoked (by unit testing it separately). Then, trust that Java will invoke your code at the right time.

I.e. extract your code into a separate class that extends Thread and test the behaviour by executing run() in a unit test.

Answer 2

In addition to Duncans answer I'd like to point out the Runtime.getRuntime().removeShutdownHook(Thread) method. Its boolean return value indicates if the respective thread was a registered hook previously.

Thus, one can test if the hook' run() method performs correctly as one part of a test. As a second part one can call Runtime.getRuntime().removeShutdownHook(Thread)` and assert that the thread was actually registered as a hook.

Together, the two tests assure the overall functioning of the shutdown hook.