@Test void ipv6_notLocalhost() {
    String ipv6 = "::2";
    Endpoint endpoint = Endpoint.newBuilder().ip(ipv6).build();

    assertThat(endpoint.ipv4())
      .isNull();
    assertThat(endpoint.ipv6())
      .isEqualTo(ipv6);
  }
This is an unusable compat Ipv4 of 0.0.0.2. This makes sure it isn't mistaken for localhost
zipkin/src/test/java/zipkin2/EndpointTest.java