test(api): make everyTick cancel test deterministic

api/main_test.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+// TestEveryTick_CallsFnOnTick verifies the helper invokes fn repeatedly on its
+// interval. A non-blocking send keeps the spawned goroutine from ever blocking
+// on a full channel, and the 1s timeout per tick is generous vs the 1ms
+// interval so the test is not timing-flaky.
+func TestEveryTick_CallsFnOnTick(t *testing.T) {
+	ctx := t.Context()
+
+	fired := make(chan struct{}, 1)
+	everyTick(ctx, time.Millisecond, func(context.Context) {
+		select {
+		case fired <- struct{}{}:
+		default:
+		}
+	})
+
+	for i := range 3 {
+		select {
+		case <-fired:
+		case <-time.After(time.Second):
+			t.Fatalf("tick %d did not fire within 1s", i+1)
+		}
+	}
+}
+
+// TestEveryTick_StopsOnContextCancel verifies cancelling ctx stops the loop.
+// After the first tick we cancel inside the inter-tick gap, so everyTick's
+// select sees only ctx.Done ready (ticker.C is cold) and returns
+// deterministically — there is no random pick between two ready cases. We then
+// confirm no further tick arrives within a full interval, which a live loop
+// could not satisfy. This is the shutdown guarantee the reconcilers depend on.
+func TestEveryTick_StopsOnContextCancel(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	const interval = 50 * time.Millisecond
+	ticks := make(chan struct{}) // unbuffered: fn blocks until the test receives
+	everyTick(ctx, interval, func(context.Context) {
+		ticks <- struct{}{}
+	})
+
+	// First tick proves the loop is running and leaves the goroutine back in
+	// select with ticker.C cold for the next ~interval.
+	select {
+	case <-ticks:
+	case <-time.After(time.Second):
+		t.Fatal("everyTick never called fn")
+	}
+
+	cancel()
+
+	// Cancel landed in the cold gap, so the loop must have taken ctx.Done and
+	// returned. A live loop would tick again at ~interval; a stopped one never
+	// will.
+	select {
+	case <-ticks:
+		t.Fatal("everyTick ticked again after cancel")
+	case <-time.After(interval + 50*time.Millisecond):
+		// good: silent past a full interval — the loop returned
+	}
+}
+
+func TestEveryTick_PassesContextToFn(t *testing.T) {
+	type ctxKey string
+	const marker ctxKey = "marker"
+	ctx, cancel := context.WithCancel(context.WithValue(context.Background(), marker, "present"))
+	defer cancel()
+
+	got := make(chan string, 1)
+	everyTick(ctx, time.Millisecond, func(c context.Context) {
+		v, _ := c.Value(marker).(string)
+		select {
+		case got <- v:
+		default:
+		}
+	})
+
+	select {
+	case v := <-got:
+		if v != "present" {
+			t.Fatalf("fn received wrong context: value = %q, want %q", v, "present")
+		}
+	case <-time.After(time.Second):
+		t.Fatalf("fn never ran")
+	}
+}