public String validateUserLoggedIn() {
    userSession.checkLoggedIn();
    return userSession.getUuid();
  }
@Test
  public void givenUserLoggedIn_whenValidateUserLoggedIn_thenReturnUserUuid() {
    // given
    String userUuid = "userUuid";
    doReturn(userUuid).when(userSession).getUuid();

    // when
    String returnedUserUuid = underTest.validateUserLoggedIn();

    // then
    assertThat(returnedUserUuid).isEqualTo(userUuid);
  }