// my code	
  @Test void test1(){
    Assertions.assertNotEquals(this, testObject);
    testObject = this;
  }
  
  // 교재 deprecated
  @Test void test1(){
    assertThat(this, is(not(sameInstance(testObject))));
    testObject = this;
  }

  static Set<JUnitTest> testObjects = new HashSet<>();
// my code
  @Test void test1(){
    Assertions.assertTrue(!testObjects.contains(this));
    testObjects.add(this);
  }
  
// 교재
  @Test void test1(){
		assertThat(testObjects, not(hasItem(this));
    testObjects.add(this);
  }