@VisibleForTesting
  static List<String> getHeaderList(final MultivaluedMap<String, String> headerMap) {
    final List<String> headers = new LinkedList<>();

    if (headerMap != null) {
      for (String key : headerMap.keySet()) {
        headers.add(key + ":" + headerMap.getFirst(key));
      }
    }

    return headers;
  }
@Test
  void testGetHeaderList() {
    assertThat(WebSocketResourceProvider.getHeaderList(new MultivaluedHashMap<>())).isEmpty();

    {
      final MultivaluedMap<String, String> headers = new MultivaluedHashMap<>();
      headers.put("test", Arrays.asList("a", "b", "c"));

      final List<String> headerStrings = WebSocketResourceProvider.getHeaderList(headers);

      assertThat(headerStrings).hasSize(1);
      assertThat(headerStrings).contains("test:a");
    }
  }