@Test
  public void prepareHeaders_ignoreIdentityEncoding() {
    Metadata m = new Metadata();
    CallOptions callOptions = CallOptions.DEFAULT.withCompressor(Codec.Identity.NONE);
    ClientCallImpl.prepareHeaders(
        m, callOptions, "user agent", DecompressorRegistry.getDefaultInstance());

    assertNull(m.get(GrpcUtil.MESSAGE_ENCODING_KEY));
  }
  @Test
  public void prepareHeaders_messageEncodingAdded() {
    Metadata m = new Metadata();
    CallOptions callOptions = CallOptions.DEFAULT.withCompressor(new Codec.Gzip());
    ClientCallImpl.prepareHeaders(
        m, callOptions, "user agent", DecompressorRegistry.getDefaultInstance());

    assertEquals(m.get(GrpcUtil.MESSAGE_ENCODING_KEY), new Codec.Gzip().getMessageEncoding());
  }