agent/cache: unit tests for ExpiryHeap, found a bug!

agent/cache/entry.go

@@ -105,11 +105,14 @@ func (h *expiryHeap) Less(i, j int) bool {
 func (h *expiryHeap) Push(x interface{}) {
 	entry := x.(*cacheEntryExpiry)
 
+	// Set initial heap index, if we're going to the end then Swap
+	// won't be called so we need to initialize
+	entry.HeapIndex = len(h.Entries)
+
 	// For the first entry, we need to trigger a channel send because
 	// Swap won't be called; nothing to swap! We can call it right away
 	// because all heap operations are within a lock.
 	if len(h.Entries) == 0 {
-		entry.HeapIndex = 0 // Set correct initial index
 		h.NotifyCh <- struct{}{}
 	}
 

agent/cache/entry_test.go

@@ -3,8 +3,89 @@ package cache
 import (
 	"container/heap"
 	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestExpiryHeap_impl(t *testing.T) {
 	var _ heap.Interface = new(expiryHeap)
 }
+
+func TestExpiryHeap(t *testing.T) {
+	require := require.New(t)
+	now := time.Now()
+	ch := make(chan struct{}, 10) // buffered to prevent blocking in tests
+	h := &expiryHeap{NotifyCh: ch}
+
+	// Init, shouldn't trigger anything
+	heap.Init(h)
+	testNoMessage(t, ch)
+
+	// Push an initial value, expect one message
+	entry := &cacheEntryExpiry{Key: "foo", HeapIndex: -1, Expires: now.Add(100)}
+	heap.Push(h, entry)
+	require.Equal(0, entry.HeapIndex)
+	testMessage(t, ch)
+	testNoMessage(t, ch) // exactly one asserted above
+
+	// Push another that goes earlier than entry
+	entry2 := &cacheEntryExpiry{Key: "bar", HeapIndex: -1, Expires: now.Add(50)}
+	heap.Push(h, entry2)
+	require.Equal(0, entry2.HeapIndex)
+	require.Equal(1, entry.HeapIndex)
+	testMessage(t, ch)
+	testNoMessage(t, ch) // exactly one asserted above
+
+	// Push another that goes at the end
+	entry3 := &cacheEntryExpiry{Key: "bar", HeapIndex: -1, Expires: now.Add(1000)}
+	heap.Push(h, entry3)
+	require.Equal(2, entry3.HeapIndex)
+	testNoMessage(t, ch) // no notify cause index 0 stayed the same
+
+	// Remove the first entry (not Pop, since we don't use Pop, but that works too)
+	remove := h.Entries[0]
+	heap.Remove(h, remove.HeapIndex)
+	require.Equal(0, entry.HeapIndex)
+	require.Equal(1, entry3.HeapIndex)
+	testMessage(t, ch)
+	testMessage(t, ch) // we have two because two swaps happen
+	testNoMessage(t, ch)
+
+	// Let's change entry 3 to be early, and fix it
+	entry3.Expires = now.Add(10)
+	h.Fix(entry3)
+	require.Equal(1, entry.HeapIndex)
+	require.Equal(0, entry3.HeapIndex)
+	testMessage(t, ch)
+	testNoMessage(t, ch)
+
+	// Let's change entry 3 again, this is an edge case where if the 0th
+	// element changed, we didn't trigger the channel. Our Fix func should.
+	entry.Expires = now.Add(20)
+	h.Fix(entry3)
+	require.Equal(1, entry.HeapIndex) // no move
+	require.Equal(0, entry3.HeapIndex)
+	testMessage(t, ch)
+	testNoMessage(t, ch) // one message
+}
+
+func testNoMessage(t *testing.T, ch <-chan struct{}) {
+	t.Helper()
+
+	select {
+	case <-ch:
+		t.Fatal("should not have a message")
+	default:
+	}
+}
+
+func testMessage(t *testing.T, ch <-chan struct{}) {
+	t.Helper()
+
+	select {
+	case <-ch:
+	default:
+		t.Fatal("should have a message")
+	}
+}