| 1 | package present_test |
| 2 | |
| 3 | import ( |
| 4 | "testing" |
| 5 | "time" |
| 6 | |
| 7 | "amadan.net/oficina/slides/internal/slides/present" |
| 8 | ) |
| 9 | |
| 10 | // recv reads one event, or fails: every assertion here is about |
| 11 | // something arriving, and a test that hangs waiting for it tells the |
| 12 | // person running it nothing. |
| 13 | func recv(t *testing.T, ch <-chan present.Event, what string) present.Event { |
| 14 | t.Helper() |
| 15 | select { |
| 16 | case e, ok := <-ch: |
| 17 | if !ok { |
| 18 | t.Fatalf("%s: the channel was closed, want an event", what) |
| 19 | } |
| 20 | return e |
| 21 | case <-time.After(2 * time.Second): |
| 22 | t.Fatalf("%s: no event within two seconds", what) |
| 23 | } |
| 24 | return present.Event{} |
| 25 | } |
| 26 | |
| 27 | // TestPublishReachesEverySubscriber: a session's event reaches every |
| 28 | // page watching that session — the presenter's laptop, the phone in |
| 29 | // their hand, and every follower — and nobody watching another one. |
| 30 | func TestPublishReachesEverySubscriber(t *testing.T) { |
| 31 | h := present.New() |
| 32 | |
| 33 | laptop, stopLaptop := h.Subscribe("talk") |
| 34 | defer stopLaptop() |
| 35 | phone, stopPhone := h.Subscribe("talk") |
| 36 | defer stopPhone() |
| 37 | elsewhere, stopElsewhere := h.Subscribe("other-talk") |
| 38 | defer stopElsewhere() |
| 39 | |
| 40 | h.Publish("talk", present.Event{Slide: 3, Blackout: true}) |
| 41 | |
| 42 | if e := recv(t, laptop, "the laptop"); e.Slide != 3 || !e.Blackout { |
| 43 | t.Errorf("the laptop got %+v, want slide 3 blacked out", e) |
| 44 | } |
| 45 | if e := recv(t, phone, "the phone"); e.Slide != 3 || !e.Blackout { |
| 46 | t.Errorf("the phone got %+v, want slide 3 blacked out", e) |
| 47 | } |
| 48 | select { |
| 49 | case e := <-elsewhere: |
| 50 | t.Errorf("a subscriber to another session got %+v", e) |
| 51 | default: |
| 52 | } |
| 53 | |
| 54 | // Cancelling really unsubscribes: the next event reaches the phone |
| 55 | // and not the laptop. |
| 56 | stopLaptop() |
| 57 | h.Publish("talk", present.Event{Slide: 4}) |
| 58 | if e := recv(t, phone, "the phone after the laptop left"); e.Slide != 4 { |
| 59 | t.Errorf("the phone got %+v, want slide 4", e) |
| 60 | } |
| 61 | select { |
| 62 | case e, ok := <-laptop: |
| 63 | if ok { |
| 64 | t.Errorf("a cancelled subscriber got %+v", e) |
| 65 | } |
| 66 | default: |
| 67 | } |
| 68 | |
| 69 | // Cancelling twice is a no-op, not a panic: the stream handler |
| 70 | // defers its stop and may also have reason to stop early. |
| 71 | stopLaptop() |
| 72 | } |
| 73 | |
| 74 | // TestSlowSubscriberIsDropped: a page that has stopped reading — a |
| 75 | // laptop asleep with the tab open — must never hold up the phone in |
| 76 | // somebody's hand. Past the buffer it is dropped, and its channel is |
| 77 | // closed so the handler holding it returns instead of blocking on a |
| 78 | // stream that will never move again. |
| 79 | func TestSlowSubscriberIsDropped(t *testing.T) { |
| 80 | h := present.New() |
| 81 | |
| 82 | slow, stopSlow := h.Subscribe("talk") |
| 83 | defer stopSlow() |
| 84 | quick, stopQuick := h.Subscribe("talk") |
| 85 | defer stopQuick() |
| 86 | |
| 87 | for i := 0; i < 12; i++ { |
| 88 | h.Publish("talk", present.Event{Slide: i}) |
| 89 | // The quick subscriber keeps up, so only the slow one is ever |
| 90 | // behind: this test is about one subscriber's back pressure, |
| 91 | // not about both. |
| 92 | if e := recv(t, quick, "the quick subscriber"); e.Slide != i { |
| 93 | t.Fatalf("the quick subscriber got %+v, want slide %d", e, i) |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | // The buffer it did get is intact — dropping is not a rewrite of |
| 98 | // what was already delivered. |
| 99 | for i := 0; i < 8; i++ { |
| 100 | if e := recv(t, slow, "the slow subscriber's buffer"); e.Slide != i { |
| 101 | t.Fatalf("the slow subscriber's buffered event %d is %+v", i, e) |
| 102 | } |
| 103 | } |
| 104 | select { |
| 105 | case _, ok := <-slow: |
| 106 | if ok { |
| 107 | t.Fatal("the slow subscriber is still delivered to past its buffer") |
| 108 | } |
| 109 | case <-time.After(2 * time.Second): |
| 110 | t.Fatal("the slow subscriber was neither delivered to nor closed") |
| 111 | } |
| 112 | |
| 113 | // And the session is still live for everyone who kept up. |
| 114 | h.Publish("talk", present.Event{Slide: 99, Ended: true}) |
| 115 | if e := recv(t, quick, "the quick subscriber at the end"); e.Slide != 99 || !e.Ended { |
| 116 | t.Errorf("the quick subscriber got %+v, want the ending event", e) |
| 117 | } |
| 118 | } |
| 119 | |
amadan