void grpcCallOptions() {
        try (ClientRequestContextCaptor ctxCaptor = Clients.newContextCaptor()) {
            blockingStub
                    .withOption(MY_CALL_OPTION_KEY, "foo")
                    .emptyCall(EMPTY);
            final ClientRequestContext ctx = ctxCaptor.get();
            assertThat(GrpcCallOptions.get(ctx).getOption(MY_CALL_OPTION_KEY)).isEqualTo("foo");
        }
    }
Must be at least {@link #unaryPayloadLength()}, plus some to account for encoding overhead.
grpc/src/test/java/com/linecorp/armeria/client/grpc/GrpcClientTest.java