// being true.
    Pattern pattern = Pattern.compile("Multiple entries with same key: four=(.*) and four=(.*)");
    assertThat(expected).hasMessageThat().matches(pattern);
      Matcher matcher = pattern.matcher(expected.getMessage());
      assertThat(matcher.matches()).isTrue();
      assertThat(matcher.group(1)).isNotEqualTo(matcher.group(2));
  }

    }
    IllegalArgumentException expected =
        assertThrows(
            IllegalArgumentException.class,
            () -> builder.addAll(nCopies(Integer.MAX_VALUE - 50, "a")));
    assertThat(expected).hasMessageThat().contains("cannot store more than MAX_VALUE elements");
  }

    // being true.
    Pattern pattern = Pattern.compile("Multiple entries with same key: four=(.*) and four=(.*)");
    assertThat(expected).hasMessageThat().matches(pattern);
      Matcher matcher = pattern.matcher(expected.getMessage());
      assertThat(matcher.matches()).isTrue();
      assertThat(matcher.group(1)).isNotEqualTo(matcher.group(2));
  }