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/geo/locator_internal_test.go

@@ -90,14 +90,12 @@ func parseAddresses(t *testing.T, addresses ...string) []netip.Addr {
 	return addrs
 }
 
-// fakeGeoJS is a geojs server. It sends body, or status when that is set, or
-// waits for the request to end when hang is true. It keeps each request's
-// address list.
+// fakeGeoJS is a geojs server. It sends body, or status when that is set. It
+// keeps each request's address list.
 type fakeGeoJS struct {
 	server *httptest.Server
 	body   string
 	status int
-	hang   bool
 
 	mu       sync.Mutex
 	requests []string
@@ -119,12 +117,6 @@ func (f *fakeGeoJS) serve(w http.ResponseWriter, r *http.Request) {
 	f.requests = append(f.requests, r.URL.Query().Get("ip"))
 	f.mu.Unlock()
 
-	if f.hang {
-		<-r.Context().Done()
-
-		return
-	}
-
 	if f.status != 0 {
 		w.WriteHeader(f.status)
 
@@ -142,6 +134,20 @@ func (f *fakeGeoJS) requestsSeen() []string {
 	return append([]string{}, f.requests...)
 }
 
+// hangingTransport never answers: each request waits until its context ends.
+// It counts the requests as they are sent, so the count does not depend on
+// whether one reaches a server before its time limit runs out.
+type hangingTransport struct {
+	requests atomic.Int32
+}
+
+func (h *hangingTransport) RoundTrip(r *http.Request) (*http.Response, error) {
+	h.requests.Add(1)
+	<-r.Context().Done()
+
+	return nil, r.Context().Err()
+}
+
 // openCacheDB opens a new cache.db in a temporary directory.
 func openCacheDB(t *testing.T, dir string) *sql.DB {
 	t.Helper()
@@ -385,13 +391,15 @@ func TestLookupFallsBackToTheDatabase(t *testing.T) {
 
 			fake := newFakeGeoJS(t, tt.body)
 			fake.status = tt.status
-			fake.hang = tt.hang
 			dir := t.TempDir()
 			locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)
-			locator.timeLimit = shortTimeLimit
+			requestCount := func() int { return len(fake.requestsSeen()) }
 
-			if !tt.hang {
-				locator.timeLimit = testTimeLimit
+			if tt.hang {
+				hanging := &hangingTransport{}
+				locator.client = &http.Client{Transport: hanging}
+				locator.timeLimit = shortTimeLimit
+				requestCount = func() int { return int(hanging.requests.Load()) }
 			}
 
 			giveDatabase(t, locator)
@@ -413,8 +421,8 @@ func TestLookupFallsBackToTheDatabase(t *testing.T) {
 			// asks geojs again.
 			lookupOne(t, locator, testAddress)
 
-			if requests := fake.requestsSeen(); len(requests) != 2 {
-				t.Errorf("%d requests, want 2", len(requests))
+			if requests := requestCount(); requests != 2 {
+				t.Errorf("%d requests, want 2", requests)
 			}
 		})
 	}