Fix race condition in test

sync2/device_data_ticker_test.go

@@ -10,12 +10,31 @@ import (
 	"github.com/matrix-org/sliding-sync/pubsub"
 )
 
+type syncSlice[T any] struct {
+	slice []T
+	mu    sync.Mutex
+}
+
+func (s *syncSlice[T]) append(item T) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.slice = append(s.slice, item)
+}
+
+func (s *syncSlice[T]) clone() []T {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	result := make([]T, len(s.slice))
+	copy(result, s.slice)
+	return result
+}
+
 func TestDeviceTickerBasic(t *testing.T) {
 	duration := time.Millisecond
 	ticker := NewDeviceDataTicker(duration)
-	var payloads []*pubsub.V2DeviceData
+	var payloads syncSlice[*pubsub.V2DeviceData]
 	ticker.SetCallback(func(payload *pubsub.V2DeviceData) {
-		payloads = append(payloads, payload)
+		payloads.append(payload)
 	})
 	var wg sync.WaitGroup
 	wg.Add(1)
@@ -31,29 +50,31 @@ func TestDeviceTickerBasic(t *testing.T) {
 		DeviceID: "b",
 	})
 	time.Sleep(duration * 2)
-	if len(payloads) != 1 {
+	result := payloads.clone()
-		t.Fatalf("expected 1 callback, got %d", len(payloads))
+	if len(result) != 1 {
+		t.Fatalf("expected 1 callback, got %d", len(result))
 	}
 	want := map[string][]string{
 		"a": {"b"},
 	}
-	assertPayloadEqual(t, payloads[0].UserIDToDeviceIDs, want)
+	assertPayloadEqual(t, result[0].UserIDToDeviceIDs, want)
 	// check stopping works
-	payloads = []*pubsub.V2DeviceData{}
+	payloads = syncSlice[*pubsub.V2DeviceData]{}
 	ticker.Stop()
 	wg.Wait()
 	time.Sleep(duration * 2)
-	if len(payloads) != 0 {
+	result = payloads.clone()
-		t.Fatalf("got extra payloads: %+v", payloads)
+	if len(result) != 0 {
+		t.Fatalf("got extra payloads: %+v", result)
 	}
 }
 
 func TestDeviceTickerBatchesCorrectly(t *testing.T) {
 	duration := 100 * time.Millisecond
 	ticker := NewDeviceDataTicker(duration)
-	var payloads []*pubsub.V2DeviceData
+	var payloads syncSlice[*pubsub.V2DeviceData]
 	ticker.SetCallback(func(payload *pubsub.V2DeviceData) {
-		payloads = append(payloads, payload)
+		payloads.append(payload)
 	})
 	go ticker.Run()
 	defer ticker.Stop()
@@ -74,23 +95,23 @@ func TestDeviceTickerBatchesCorrectly(t *testing.T) {
 		DeviceID: "y", // new device and user
 	})
 	time.Sleep(duration * 2)
-	if len(payloads) != 1 {
+	result := payloads.clone()
-		t.Fatalf("expected 1 callback, got %d", len(payloads))
+	if len(result) != 1 {
+		t.Fatalf("expected 1 callback, got %d", len(result))
 	}
 	want := map[string][]string{
 		"a": {"b", "bb"},
 		"x": {"y"},
 	}
-	assertPayloadEqual(t, payloads[0].UserIDToDeviceIDs, want)
+	assertPayloadEqual(t, result[0].UserIDToDeviceIDs, want)
 }
 
 func TestDeviceTickerForgetsAfterEmitting(t *testing.T) {
 	duration := time.Millisecond
 	ticker := NewDeviceDataTicker(duration)
-	var payloads []*pubsub.V2DeviceData
+	var payloads syncSlice[*pubsub.V2DeviceData]
-
 	ticker.SetCallback(func(payload *pubsub.V2DeviceData) {
-		payloads = append(payloads, payload)
+		payloads.append(payload)
 	})
 	ticker.Remember(PollerID{
 		UserID:   "a",
@@ -104,8 +125,9 @@ func TestDeviceTickerForgetsAfterEmitting(t *testing.T) {
 		DeviceID: "b",
 	})
 	time.Sleep(10 * duration)
-	if len(payloads) != 1 {
+	result := payloads.clone()
-		t.Fatalf("got %d payloads, want 1", len(payloads))
+	if len(result) != 1 {
+		t.Fatalf("got %d payloads, want 1", len(result))
 	}
 }