Add tests for MSC4102 (#709)

* Add failing test for matrix-org/matrix-spec#1727

* Logs are fun

* Update with semantics of MSC4102

* Also test over federation

tests/csapi/thread_notifications_test.go

@@ -301,3 +301,54 @@ func TestThreadedReceipts(t *testing.T) {
 		}),
 	)
 }
+
+// Regression test for https://github.com/matrix-org/matrix-spec/issues/1727
+// Servers should always prefer the unthreaded receipt when there is a clash of receipts
+func TestThreadReceiptsInSyncMSC4102(t *testing.T) {
+	runtime.SkipIf(t, runtime.Dendrite) // not supported
+	deployment := complement.Deploy(t, 2)
+	defer deployment.Destroy(t)
+
+	// Create a room with alice and bob.
+	alice := deployment.Register(t, "hs1", helpers.RegistrationOpts{})
+	bob := deployment.Register(t, "hs2", helpers.RegistrationOpts{})
+	roomID := alice.MustCreateRoom(t, map[string]interface{}{"preset": "public_chat"})
+	bob.MustJoinRoom(t, roomID, []string{"hs1"})
+	eventA := alice.SendEventSynced(t, roomID, b.Event{
+		Type: "m.room.message",
+		Content: map[string]interface{}{
+			"msgtype": "m.text",
+			"body":    "Hello world!",
+		},
+	})
+	eventB := alice.SendEventSynced(t, roomID, b.Event{
+		Type: "m.room.message",
+		Content: map[string]interface{}{
+			"msgtype": "m.text",
+			"body":    "Start thread!",
+			"m.relates_to": map[string]interface{}{
+				"event_id": eventA,
+				"rel_type": "m.thread",
+			},
+		},
+	})
+	// now send an unthreaded RR for event B and a threaded RR for event B and ensure we see the unthreaded RR
+	// down /sync. Non-compliant servers will typically send the last one only.
+	alice.MustDo(t, "POST", []string{"_matrix", "client", "v3", "rooms", roomID, "receipt", "m.read", eventB}, client.WithJSONBody(t, struct{}{}))
+	alice.MustDo(t, "POST", []string{"_matrix", "client", "v3", "rooms", roomID, "receipt", "m.read", eventB}, client.WithJSONBody(t, map[string]interface{}{"thread_id": eventA}))
+
+	alice.MustSyncUntil(
+		t,
+		client.SyncReq{},
+		syncHasUnthreadedReadReceipt(roomID, alice.UserID, eventB),
+	)
+
+	// bob over federation must also see the same result, to show that the receipt EDUs over
+	// federation are bundled correctly, or are sent as separate EDUs.
+	bob.MustSyncUntil(
+		t,
+		client.SyncReq{},
+		syncHasUnthreadedReadReceipt(roomID, alice.UserID, eventB),
+	)
+
+}