test: prove queued snapshot stays within byte budget

tests/logger/queue_test.go

@@ -358,6 +358,41 @@ func TestQueueSubmitOwnsEntrySnapshot(t *testing.T) {
 	}
 }
 
+func TestQueueByteBudgetTracksOwnedEntrySnapshot(t *testing.T) {
+	batch := &fakeBatch{}
+	backend := newQueueBackend(func(context.Context, string) (logger.Batch, error) {
+		return batch, nil
+	})
+	entry := &logger.LogEntry{RequestID: "original", RequestBody: []byte("body")}
+	budget := logger.EstimatedBytes(entry)
+	q := logger.NewQueueWithBackend(backend, 2, 1, 1, time.Hour, budget)
+
+	q.Submit(entry)
+	entry.RequestID = "mutated"
+	entry.RequestBody = []byte("body expanded after submission")
+	q.Submit(&logger.LogEntry{RequestID: "x"})
+
+	if stats := q.Stats(); stats.Enqueued != 1 || stats.Dropped != 1 || stats.Bytes != budget {
+		t.Fatalf("before flush: %+v budget=%d", stats, budget)
+	}
+
+	q.Start(context.Background())
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	if err := q.Stop(ctx); err != nil {
+		t.Fatalf("Stop: %v", err)
+	}
+	if len(batch.rows) != 1 {
+		t.Fatalf("written rows=%d want 1", len(batch.rows))
+	}
+	if row := batch.rows[0]; row[0] != "original" || row[6] != "body" {
+		t.Fatalf("written row does not match budgeted snapshot: %#v", row)
+	}
+	if stats := q.Stats(); stats.Bytes != 0 {
+		t.Fatalf("after flush: %+v", stats)
+	}
+}
+
 func TestQueueCanceledStopEventuallyReleasesAllBudget(t *testing.T) {
 	entry := &logger.LogEntry{RequestID: "queued"}
 	q := logger.NewQueue(nil, 32, 32, 1, time.Hour, 32*logger.EstimatedBytes(entry))