static void runHook() {
        for (String filename : FILES) {
            new File(filename).delete();
        }
    }
@Test
    public void testSimulateTriggerDeleteFileOnExitHook() {

        // simulate app exit
        DeleteFileOnExitHook.runHook();

        File[] files = new File(HOOK_TEST_TMP).listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
                return name.startsWith(DiskFileUpload.prefix);
            }
        });

        assertEquals(0, files.length);
    }