@Test
    void preprocessor() throws Exception {
        final TestServiceBlockingStub stub =
                GrpcClients.newClient(HttpPreprocessor.of(SessionProtocol.HTTP, server.httpEndpoint()),
                                      TestServiceBlockingStub.class);
        assertThat(stub.emptyCall(EMPTY)).isEqualTo(EMPTY);
    }
Must be at least {@link #unaryPayloadLength()}, plus some to account for encoding overhead.
grpc/src/test/java/com/linecorp/armeria/client/grpc/GrpcClientTest.java