Make two tests independent of host load (closes #256)

The home-card refresh test runs keepHomeCardsFresh in a synctest bubble,
so its waits are exact on a fake clock instead of 15-second polls.

The geo fallback subtest in which geojs never answers used a 50 ms time
limit and counted requests at the fake server, which a slow host could
miss. It now uses a transport that counts each request as it is sent and
holds it until the time limit ends it.

Model: opus-5-5

internal/server/home_internal_test.go

@@ -275,49 +275,66 @@ func TestPagesServeTheCopyOfTheCards(t *testing.T) {
 	}
 }
 
-// TestKeepHomeCardsFreshWorksThemOutEveryInterval runs keepHomeCardsFresh with
-// a short interval. It works the cards out at once, again after the table
-// changes, and stops when its context ends.
+// TestKeepHomeCardsFreshWorksThemOutEveryInterval runs keepHomeCardsFresh. It
+// works the cards out at once, again an interval after the table changes, and
+// stops when its context ends. It runs in a synctest bubble, whose clock is
+// fake, so a stall on the host cannot fail it.
 func TestKeepHomeCardsFreshWorksThemOutEveryInterval(t *testing.T) {
 	t.Parallel()
 
-	const (
-		interval = 10 * time.Millisecond
-		maxWait  = 15 * time.Second
-	)
+	const interval = time.Minute
 
 	table := emptyTable()
 	announce(table, "1.0.0.0/24", twoPrefixASN, testPeer(1), testRouteTime(0))
 
 	s := newServerWithTable(t, table)
 
-	ctx, cancel := context.WithCancel(t.Context())
-	stopped := make(chan struct{})
-
-	go func() {
-		s.keepHomeCardsFresh(ctx, interval)
-		close(stopped)
-	}()
-
-	newestRouteASNIs := func(asn int) bool {
+	// newestRouteOrigin returns the origin AS of the newest route on the
+	// cards, or 0 when there is none.
+	newestRouteOrigin := func() int {
 		cards := s.cards.Load()
+		if cards == nil || cards.NewestRoute == nil {
+			return 0
+		}
 
-		return cards != nil && cards.NewestRoute != nil &&
-			cards.NewestRoute.OriginASN == asn
+		return cards.NewestRoute.OriginASN
 	}
 
-	waitUntil(t, maxWait, func() bool { return newestRouteASNIs(twoPrefixASN) })
+	synctest.Test(t, func(t *testing.T) {
+		ctx, cancel := context.WithCancel(t.Context())
+		stopped := make(chan struct{})
 
-	announce(table, "8.8.8.0/24", newestRouteASN, testPeer(2), testRouteTime(1))
-	waitUntil(t, maxWait, func() bool { return newestRouteASNIs(newestRouteASN) })
+		go func() {
+			s.keepHomeCardsFresh(ctx, interval)
+			close(stopped)
+		}()
 
-	cancel()
+		synctest.Wait()
 
-	select {
-	case <-stopped:
-	case <-time.After(maxWait):
-		t.Fatal("keepHomeCardsFresh did not stop when its context ended")
-	}
+		if got := newestRouteOrigin(); got != twoPrefixASN {
+			t.Fatalf("at the start, the newest route's AS is %d, want %d",
+				got, twoPrefixASN)
+		}
+
+		announce(table, "8.8.8.0/24", newestRouteASN, testPeer(2),
+			testRouteTime(1))
+		time.Sleep(interval)
+		synctest.Wait()
+
+		if got := newestRouteOrigin(); got != newestRouteASN {
+			t.Fatalf("an interval after the table changed, the newest "+
+				"route's AS is %d, want %d", got, newestRouteASN)
+		}
+
+		cancel()
+		synctest.Wait()
+
+		select {
+		case <-stopped:
+		default:
+			t.Fatal("keepHomeCardsFresh did not stop when its context ended")
+		}
+	})
 }
 
 // TestStartedServerWorksOutTheCards starts a server and waits until its home