thread2.callAndAssertReturns(false, tryEnter());
    thread1.callAndAssertReturns(leave());
    thread2.callAndAssertReturns(false, tryEnter());
    thread1.callAndAssertReturns(leave());
    thread2.callAndAssertReturns(true, tryEnter());
  }

  public final void testSystemStateMethods() throws Exception {
    checkSystemStateMethods(0);
    thread1.callAndAssertReturns(enter());
    checkSystemStateMethods(1);

    }
  }

  /**
   * Causes this thread to call the named void method, and asserts that the call returns normally.
   */
  public void callAndAssertReturns(String methodName, Object... arguments) throws Exception {
    checkNotNull(methodName);
    checkNotNull(arguments);
    sendRequest(methodName, arguments);
    assertSame(null, getResponse(methodName).getResult());

    }
  }

  /**
   * Causes this thread to call the named void method, and asserts that the call returns normally.
   */
  public void callAndAssertReturns(String methodName, Object... arguments) throws Exception {
    checkNotNull(methodName);
    checkNotNull(arguments);
    sendRequest(methodName, arguments);
    assertSame(null, getResponse(methodName).getResult());