@Test
public void testMergeHeaders() {

  Map<String, List<String>> headers1 = createHeaders("key1", "value1", "key1", "value2");
  Map<String, List<String>> headers2 = createHeaders("key1", "value2", "key2", "value2");
  Map<String, List<String>> mergedHeaders = Headers.mergeHeaders(headers1, headers2);
  Map<String, List<String>> expectedHeaders =
      createHeaders("key1", "value1", "key1", "value2", "key1", "value2", "key2", "value2");
  assertThat(mergedHeaders).containsExactlyEntriesIn(expectedHeaders);
}