message: Reformat streaming unit test
diff: @@ -278,7 +278,7 @@ CAF_TEST(depth2_pipeline) {
  expect((std::string), from(self).to(source).with("test.txt"));
  CAF_CHECK(!deref(source).streams().empty());
  CAF_CHECK(deref(sink).streams().empty());
  - // source ----(stream_msgreturn ::open)----> sink
  + // source ----(stream_msg::open)----> sink
  expect((stream_msg::open), from(self).to(sink).with(_, source, _, _, false));
  // source <----(stream_msg::ack_open)------ sink
  expect((stream_msg::ack_open), from(sink).to(source).with(5, _, false));
  @@ -386,8 +386,9 @@ CAF_TEST(depth2_pipeline_streamer) {
  auto source = sys.spawn(streamer, sink);
  // run initialization code
  sched.run_once();
  - // source ----(stream_msgreturn ::open)----> sink
  - expect((stream_msg::open), from(source).to(sink).with(_, source, _, _, false));
  + // source ----(stream_msg::open)----> sink
  + expect((stream_msg::open),
  + from(source).to(sink).with(_, source, _, _, false));
  // source <----(stream_msg::ack_open)------ sink
  expect((stream_msg::ack_open), from(sink).to(source).with(5, _, false));
  // source ----(stream_msg::batch)---> sink
  @@ -413,8 +414,9 @@ CAF_TEST(stream_without_result) {
  auto source = sys.spawn(streamer_without_result, sink);
  // run initialization code
  sched.run_once();
  - // source ----(stream_msgreturn ::open)----> sink
  - expect((stream_msg::open), from(source).to(sink).with(_, source, _, _, false));
  + // source ----(stream_msg::open)----> sink
  + expect((stream_msg::open),
  + from(source).to(sink).with(_, source, _, _, false));
  // source <----(stream_msg::ack_open)------ sink
  expect((stream_msg::ack_open), from(sink).to(source).with(5, _, false));
  // source ----(stream_msg::batch)---> sink
  