@Override
  public String toString() {
    return entrySet().stream().map(this::toString).collect(Collectors.joining(", ", "{", "}"));
  }
@Test
  public void testToString() {
    CharSequenceMap<String> map = CharSequenceMap.create();

    // empty map
    assertThat(map.toString()).isEqualTo("{}");

    // single entry
    map.put("key1", "value1");
    assertThat(map.toString()).isEqualTo("{key1=value1}");

    // multiple entries
    map.put("key2", "value2");
    map.put("key3", "value3");
    String toStringResult = map.toString();
    assertThat(toStringResult).contains("key1=value1", "key2=value2", "key3=value3");
  }