Given tests: order arrivals by limiter state instead of sleeps (limiter, spread, cancel-while-queued)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/plans/v1/_files/internal/limiter/limiter_test.go

@@ -39,10 +39,7 @@ func TestParallelAndQueue(t *testing.T) {
 		}
 		got3 <- err
 	}()
-	time.Sleep(20 * time.Millisecond)
-	if l.Queued("alpha", "m") != 1 {
-		t.Errorf("queued = %d, want 1", l.Queued("alpha", "m"))
-	}
+	waitUntil(t, func() bool { return l.Queued("alpha", "m") == 1 })
 	// Fourth finds the queue full and is refused at once.
 	start := time.Now()
 	_, _, err = l.Acquire(ctx, "alpha", "m")
@@ -52,8 +49,8 @@ func TestParallelAndQueue(t *testing.T) {
 	if time.Since(start) > 50*time.Millisecond {
 		t.Errorf("a full queue must refuse immediately, took %v", time.Since(start))
 	}
-	time.Sleep(30 * time.Millisecond)
-	rel1() // frees a slot: the queued third proceeds
+	time.Sleep(50 * time.Millisecond) // a lower bound on the third's wait, checked above as >= 40 ms
+	rel1()                            // frees a slot: the queued third proceeds
 	select {
 	case err := <-got3:
 		if err != nil {
@@ -95,7 +92,7 @@ func TestCancelWhileQueuedLeaksNothing(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	done := make(chan error, 1)
 	go func() { _, _, err := l.Acquire(ctx, "h", "m"); done <- err }()
-	time.Sleep(20 * time.Millisecond)
+	waitUntil(t, func() bool { return l.Queued("h", "m") == 1 })
 	cancel()
 	select {
 	case err := <-done:
@@ -139,7 +136,7 @@ func TestQueueIsFIFO(t *testing.T) {
 			time.Sleep(5 * time.Millisecond)
 			r()
 		}(i)
-		time.Sleep(15 * time.Millisecond) // stagger arrivals so the order is defined
+		waitUntil(t, func() bool { return l.Queued("h", "m") == i }) // arrivals in order, by observation
 	}
 	rel()
 	wg.Wait()
@@ -176,3 +173,16 @@ func TestFreeSlotsSumsModels(t *testing.T) {
 		t.Errorf("unknown host has no slots")
 	}
 }
+
+// waitUntil polls cond every millisecond for up to two seconds and fails the test if it never holds.
+func waitUntil(t *testing.T, cond func() bool) {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if cond() {
+			return
+		}
+		time.Sleep(time.Millisecond)
+	}
+	t.Fatal("condition not reached within two seconds")
+}