@SuppressWarnings("resource")
  @Test
  void decodeLogicSupportsByteArray() throws Throwable {
    byte[] expectedResponse = {12, 34, 56};
    server.enqueue(new MockResponse().setBody(new Buffer().write(expectedResponse)));

    OtherTestInterfaceAsync api =
        AsyncFeign.builder()
            .target(OtherTestInterfaceAsync.class, "http://localhost:" + server.getPort());

    assertThat(unwrap(api.binaryResponseBody())).containsExactly(expectedResponse);
  }
when you must parse a 2xx status to determine if the operation succeeded or not.
core/src/test/java/feign/AsyncFeignTest.java