Method fixture

libcaf_net/caf/net/http/client.test.cpp:106–117

struct fixture {
  fixture() {
    mpx = net::multiplexer::make(nullptr);
    if (auto err = mpx->init()) {
      CAF_RAISE_ERROR("mpx->init failed");
    }
    mpx_thread = mpx->launch();
    auto fd_pair = net::make_stream_socket_pair();
    if (!fd_pair) {
      CAF_RAISE_ERROR("make_stream_socket_pair failed");
    }
    std::tie(fd1, fd2) = *fd_pair;
  }

  ~fixture() {
    mpx->shutdown();