R78: hybrid Clear flush, reauth reacquire, pool CAS

internal/cache/backends/review_r78_test.go

@@ -0,0 +1,55 @@
+package backends
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestHybridBackend_Clear_DrainsAsyncWrites is a regression for Hybrid.Clear
+// landing buffered async L2 writes AFTER the wipe — a key from a Set that
+// preceded Clear being resurrected into L2. Clear must flush the pending
+// async-write buffer (and block the worker) before clearing both levels.
+// We queue many non-critical keys (routed to the async L2 write path),
+// immediately Clear, then assert none ever reappears.
+func TestHybridBackend_Clear_DrainsAsyncWrites(t *testing.T) {
+	primary := newMockBackend()
+	secondary := newMockBackend()
+	hybrid, err := NewHybridBackend(&HybridConfig{
+		Primary:         primary,
+		Secondary:       secondary,
+		AsyncBufferSize: 4096,
+		Logger:          NewTestLogger(t),
+	})
+	require.NoError(t, err)
+	defer hybrid.Close()
+
+	ctx := context.Background()
+	const n = 400
+	keys := make([]string, 0, n)
+	for i := 0; i < n; i++ {
+		k := fmt.Sprintf("r78-clear-%d", i)
+		keys = append(keys, k)
+		require.NoError(t, hybrid.Set(ctx, k, []byte("v"), time.Minute), "Set")
+	}
+	// No sleep: Clear itself must drain the pending buffer.
+	require.NoError(t, hybrid.Clear(ctx), "Clear")
+
+	// Poll long enough that a stray post-Clear write would surface; fail the
+	// moment any key reappears. On the buggy code the async worker writes
+	// the buffered keys into L2 after Clear and they show up here.
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		for _, k := range keys {
+			ex, err := hybrid.Exists(ctx, k)
+			require.NoError(t, err)
+			if ex {
+				t.Fatalf("key %q resurrected after Clear", k)
+			}
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+}