@Test
  void reasonPhraseInHeader() throws IOException, InterruptedException {
    server.enqueue(
        new MockResponse()
            .addHeader("Reason-Phrase", "There is A reason")
            .setStatus("HTTP/1.1 " + 200));

    final AbstractClientTest.TestInterface api =
        newBuilder()
            .target(AbstractClientTest.TestInterface.class, "http://localhost:" + server.getPort());

    final Response response = api.post("foo");

    assertThat(response.status()).isEqualTo(200);
    assertThat(response.reason()).isEqualTo("There is A reason");
  }
Tests client-specific behavior, such as ensuring Content-Length is sent when specified.
java11/src/test/java/feign/http2client/test/Http2ClientTest.java