message: Add unit test for new fan_out_request
diff: #include "caf/test/dsl.hpp"
  #include "caf/event_based_actor.hpp"
  +#include "caf/policy/fan_in_responses.hpp"
  using namespace caf;
  @@ -150,4 +151,31 @@ CAF_TEST(delegated request with integer result) {
  CAF_CHECK_EQUAL(*result, 3);
  }
  +CAF_TEST(requesters support fan_out_request) {
  + using policy::fan_in_responses;
  + std::vector<adding_server_type> workers{
  + adding_server = make_server([](int x, int y) { return x + y; }),
  + adding_server = make_server([](int x, int y) { return x + y; }),
  + adding_server = make_server([](int x, int y) { return x + y; }),
  + };
  + run();
  + auto sum = std::make_shared<int>(0);
  + auto client = sys.spawn([=](event_based_actor* self) {
  + self->fan_out_request<fan_in_responses>(workers, infinite, 1, 2)
  + .then([=](std::vector<int> results) {
  + for (auto result : results)
  + CAF_CHECK_EQUAL(result, 3);
  + *sum = std::accumulate(results.begin(), results.end(), 0);
  + });
  + });
  + run_once();
  + expect((int, int), from(client).to(workers[0]).with(1, 2));
  + expect((int, int), from(client).to(workers[1]).with(1, 2));
  + expect((int, int), from(client).to(workers[2]).with(1, 2));
  + expect((int), from(client).to(workers[0]).with(3));
  + expect((int), from(client).to(workers[1]).with(3));
  + expect((int), from(client).to(workers[2]).with(3));
  + CAF_CHECK_EQUAL(*sum, 9);
  +}
  +
  CAF_TEST_FIXTURE_SCOPE_END()
  