@Test
public void testActivate() {

    Map<String, Object> props = new HashMap<>();
    props.put("poolSize", 0);
    manager.modified(props);
    ForkJoinPool pool = Whitebox.getInternalState(manager, "threadPool");
    assertTrue(pool.getParallelism() > 0);
    props.put("poolSize", -1);
    manager.modified(props);
    pool = Whitebox.getInternalState(manager, "threadPool");
    assertEquals(pool.getParallelism(), 1);
    props.put("poolSize", 1);
    manager.modified(props);
    pool = Whitebox.getInternalState(manager, "threadPool");
    assertEquals(pool.getParallelism(), 1);
    props.put("poolSize", 2);
    manager.modified(props);
    pool = Whitebox.getInternalState(manager, "threadPool");
    assertEquals(pool.getParallelism(), 2);
}