private void assertConnected(Activity activity) {
    Collection transitions = flow.getBegin().getLeavingTransitions();
    assertTrue(transitions.contains(activity.getDefaultArrivingTransition()));

    transitions = flow.getEnd().getArrivingTransitions();
    assertTrue(transitions.contains(activity.getDefaultLeavingTransition()));
  }
  public void testRemoveNode() {
    // remove first, middle and last activities
    flow.addNode(first);
    flow.addNode(second);

    flow.removeNode(first);
    assertDisconnected(first);
    flow.removeNode(second);
    assertDisconnected(second);

    assertEquals(0, flow.getBegin().getLeavingTransitions().size());
    assertEquals(0, flow.getEnd().getArrivingTransitions().size());
  }