public static boolean isValidProjectKey(String keyCandidate) {
    return VALID_PROJECT_KEY_REGEXP.matcher(keyCandidate).matches();
  }
@Test
  public void invalid_project_key() {
    assertThat(ComponentKeys.isValidProjectKey("0123")).isFalse();

    assertThat(ComponentKeys.isValidProjectKey("ab/12")).isFalse();
    assertThat(ComponentKeys.isValidProjectKey("코드품질")).isFalse();

    assertThat(ComponentKeys.isValidProjectKey("")).isFalse();
    assertThat(ComponentKeys.isValidProjectKey(" ")).isFalse();
    assertThat(ComponentKeys.isValidProjectKey("ab 12")).isFalse();
    assertThat(ComponentKeys.isValidProjectKey(" ab")).isFalse();
    assertThat(ComponentKeys.isValidProjectKey("ab ")).isFalse();
  }