@Test
  public void nullAuthenticatorShouldReturnNull() throws Exception {
    assertThat(securityProps).doesNotContainKey(SECURITY_PEER_AUTHENTICATOR);
    String result =
        authenticator.authenticate(member, securityProps, securityProps);
    // assertThat(result).isNull(); NOTE: old security used to return null
    assertThat(result).contains("Security check failed");
  }
Unit tests GMSAuthenticator using old security.
geode-core/src/test/java/org/apache/geode/distributed/internal/membership/adapter/auth/GMSAuthenticatorWithAuthenticatorTest.java