Method handlerError

test/cpp/src/TestServer.cpp:400–402

    communicate("asyncComplete", ctx, fn_name);
  }
  void handlerError(void* ctx, const char* fn_name) override {
    communicate("handlerError", ctx, fn_name);
  }

  void communicate(const char* event, void* ctx, const char* fn_name) {
    std::cout << event << ": " << *static_cast<std::string*>(ctx) << " = " << fn_name << '\n';