public Map<String, String> tags() {
    return UnsafeArrayMap.<String, String>newBuilder().build(tags);
  }
@Test void tags() {
    MutableSpan span = new MutableSpan();
    assertThat(span.tagCount()).isZero();
    assertThat(span.tags()).isEmpty();

    span.tag("http.method", "GET");
    assertThat(span.tagCount()).isOne();
    assertThat(span.tags()).containsExactly(
        entry("http.method", "GET")
    );

    span.tag("error", "500");
    assertThat(span.tagCount()).isEqualTo(2);
    assertThat(span.tags()).containsExactly(
        entry("http.method", "GET"),
        entry("error", "500")
    );

    span.forEachTag((t, v) -> v.equals("GET") ? v : null);
    assertThat(span.tagCount()).isOne();
    assertThat(span.tags()).containsExactly(
        entry("http.method", "GET")
    );
  }