content test [nfc]: Have prepareContentBare give pointer to pushed routes

Author: chrisbobbe

test/widgets/content_test.dart

@@ -92,7 +92,7 @@ void main() {
 
   TestZulipBinding.ensureInitialized();
 
-  Future<void> prepareContentBare(WidgetTester tester, String html, {
+  Future<List<Route<dynamic>>> prepareContentBare(WidgetTester tester, String html, {
     bool wrapWithScaffold = false,
     bool wrapWithPerAccountStoreWidget = false,
   }) async {
@@ -110,17 +110,28 @@ void main() {
     widget = GlobalStoreWidget(child: widget);
     addTearDown(testBinding.reset);
 
+    final pushedRoutes = <Route<dynamic>>[];
+    final testNavObserver = TestNavigatorObserver()
+      ..onPushed = (route, prevRoute) => pushedRoutes.add(route);
+
     await tester.pumpWidget(
       Builder(builder: (context) =>
         MaterialApp(
           theme: ThemeData(typography: zulipTypography(context)),
           localizationsDelegates: ZulipLocalizations.localizationsDelegates,
           supportedLocales: ZulipLocalizations.supportedLocales,
+          navigatorObservers: [testNavObserver],
           home: widget)));
     await tester.pump(); // global store
     if (wrapWithPerAccountStoreWidget) {
       await tester.pump();
     }
+
+    // `tester.pumpWidget` introduces an initial route;
+    // remove it so consumers only have newly pushed routes.
+    assert(pushedRoutes.length == 1);
+    pushedRoutes.removeLast();
+    return pushedRoutes;
   }
 
   /// Test that the given content example renders without throwing an exception.