@Test
public void givenHashMap_whenEquals_thenTrue() {
    Map``<String, Integer>`` map = new HashMap<>();
    
    // 将键值对放入我们的map中。
    map.put("first", 1);
    map.put(null, 2);
    map.put("third", null);
    
    // 断言语句。最后一个参数是如果断言失败将打印的内容。
    assertNotNull(map, "The HashMap is null!");
    assertEquals(1, map.get("first"), "The key isn't mapped to the right value!");
    assertEquals(2, map.get(null), "HashMap didn't accept null as key!");
    assertEquals(null, map.get("third"), "HashMap didn't accept null value!");
}