messenger: count the store's writes, and name an ask's record when it is the only one held (review of issue 422)

The review's two nits. A write of bytes identical to what is stored was
invisible to a comparison of content, so the test store counts its
writes and the preview's tests read that count: a persist from inside
Preview now fails five of them instead of one. And a router holding an
ask's record and no condition said it held none, rather than saying what
that key is; the branches are the other way round, with a test that
holds nothing else.

modules/messenger/cmd/messenger/holder_test.go

@@ -66,6 +66,8 @@ func (f *fakeChannel) Edit(id string, m Message) error {
 type memStore struct {
 	recs   map[string]Record
 	recent []Sent
+	// puts counts the writes, so a write of bytes identical to what is stored is still seen (issue 422's review).
+	puts int
 }
 
 func (m *memStore) Put(r Record) error {
@@ -73,6 +75,7 @@ func (m *memStore) Put(r Record) error {
 		m.recs = map[string]Record{}
 	}
 	m.recs[r.Key] = r
+	m.puts++
 	return nil
 }
 func (m *memStore) Delete(k string) error { delete(m.recs, k); return nil }

modules/messenger/cmd/messenger/preview.go

@@ -68,11 +68,14 @@ func (h *Holder) Preview(key, what string) (map[string]any, error) {
 	if !holding || r.Origin != "condition" {
 		sort.Strings(conditions)
 		switch {
-		case len(conditions) == 0:
+		case holding && len(conditions) == 0:
-			return nil, errorf("no condition %s is open here, and this router holds none: `mesh-controller.conditions` says what the controller holds open", key)
+			return nil, errorf("%s is not a condition but this router's own %s record, which is said as part of an ask, never on its own; it holds no condition",
+				key, r.Origin)
 		case holding:
 			return nil, errorf("%s is not a condition but this router's own %s record, which is said as part of an ask, never on its own; it holds the conditions %s",
 				key, r.Origin, strings.Join(conditions, ", "))
+		case len(conditions) == 0:
+			return nil, errorf("no condition %s is open here, and this router holds none: `mesh-controller.conditions` says what the controller holds open", key)
 		default:
 			return nil, errorf("no condition %s is open here; it holds %s", key, strings.Join(conditions, ", "))
 		}

modules/messenger/cmd/messenger/preview_test.go

@@ -33,9 +33,9 @@ func previewHolder(t *testing.T, issues []TrackedIssue) (*Holder, *fakeChannel,
 // unmoved fails when anything a send would move has moved: the sends, the queue, the history, what is
 // stored, and the record itself.
 type unmoved struct {
-	sends, queued, recent, refusals int
+	sends, queued, recent, refusals, puts int
-	stored                          Record
+	stored                                Record
-	held                            Record
+	held                                  Record
 }
 
 func mark(t *testing.T, h *Holder, tg, dt *fakeChannel, st *memStore, key string) unmoved {
@@ -47,7 +47,7 @@ func mark(t *testing.T, h *Holder, tg, dt *fakeChannel, st *memStore, key string
 		queued += len(list)
 	}
 	return unmoved{sends: len(tg.sends) + len(dt.sends), queued: queued, recent: len(h.recent),
-		refusals: len(h.refusals), stored: st.recs[key], held: *h.open[key]}
+		refusals: len(h.refusals), puts: st.puts, stored: st.recs[key], held: *h.open[key]}
 }
 
 func (was unmoved) check(t *testing.T, h *Holder, tg, dt *fakeChannel, st *memStore, c *clock, key string) {
@@ -66,6 +66,9 @@ func (was unmoved) check(t *testing.T, h *Holder, tg, dt *fakeChannel, st *memSt
 	if now.refusals != was.refusals {
 		t.Errorf("a preview recorded %d refusal(s): only a send does that", now.refusals-was.refusals)
 	}
+	if now.puts != was.puts {
+		t.Errorf("a preview wrote to the store %d time(s), even if the bytes were the same", now.puts-was.puts)
+	}
 	if !reflect.DeepEqual(now.stored, was.stored) {
 		t.Errorf("a preview wrote the record: %+v", now.stored)
 	}
@@ -204,9 +207,19 @@ func TestAPreviewOfWhatThisRouterDoesNotHoldIsRefusedByName(t *testing.T) {
 	h.open["ask.someone.1"] = &Record{Key: "ask.someone.1", Origin: "ask", Severity: Urgent, Summary: "a question"}
 	h.mu.Unlock()
 	_, err = h.Preview("ask.someone.1", "")
-	if err == nil || !strings.Contains(err.Error(), "not a condition") {
+	if err == nil || !strings.Contains(err.Error(), "not a condition") || !strings.Contains(err.Error(), k.Key) {
 		t.Errorf("an ask's record previewed as a condition: %v", err)
 	}
+
+	// A router holding an ask and no condition says what that key is, not that it holds nothing.
+	bare, _, _, _, _ := newHolder(t)
+	bare.mu.Lock()
+	bare.open["ask.someone.2"] = &Record{Key: "ask.someone.2", Origin: "ask", Severity: Urgent, Summary: "a question"}
+	bare.mu.Unlock()
+	_, err = bare.Preview("ask.someone.2", "")
+	if err == nil || !strings.Contains(err.Error(), "not a condition") {
+		t.Errorf("the only record held is an ask's: %v", err)
+	}
 }
 
 func TestAPreviewAsksTheTrackerWhenItsWordWentCold(t *testing.T) {