test: add tests for navigator observer

pubspec.yaml

@@ -15,6 +15,7 @@ dependencies:
 
 dev_dependencies:
   build_runner: ^2.0.3
+  fake_async: '>=1.2.0 <1.4.0'
   flutter_test:
     sdk: flutter
   lint: ^1.0.0

test/utils/instabug_navigator_observer_test.dart

@@ -0,0 +1,98 @@
+import 'package:fake_async/fake_async.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:instabug_flutter/instabug_flutter.dart';
+import 'package:instabug_flutter/src/generated/instabug.api.g.dart';
+import 'package:instabug_flutter/src/utils/screen_loading/screen_loading_manager.dart';
+import 'package:mockito/annotations.dart';
+import 'package:mockito/mockito.dart';
+
+import 'instabug_navigator_observer_test.mocks.dart';
+
+@GenerateMocks([
+  InstabugHostApi,
+  ScreenLoadingManager,
+])
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  WidgetsFlutterBinding.ensureInitialized();
+
+  final mHost = MockInstabugHostApi();
+  final mScreenLoadingManager = MockScreenLoadingManager();
+
+  late InstabugNavigatorObserver observer;
+  const screen = '/screen';
+  const previousScreen = '/previousScreen';
+  late Route route;
+  late Route previousRoute;
+
+  setUpAll(() {
+    Instabug.$setHostApi(mHost);
+    ScreenLoadingManager.setInstance(mScreenLoadingManager);
+  });
+
+  setUp(() {
+    observer = InstabugNavigatorObserver();
+    route = createRoute(screen);
+    previousRoute = createRoute(previousScreen);
+  });
+
+  test('should report screen change when a route is pushed', () {
+    fakeAsync((async) {
+      observer.didPush(route, previousRoute);
+
+      async.elapse(const Duration(milliseconds: 1000));
+
+      verify(
+        mScreenLoadingManager.startUiTrace(screen),
+      ).called(1);
+
+      verify(
+        mHost.reportScreenChange(screen),
+      ).called(1);
+    });
+  });
+
+  test(
+      'should report screen change when a route is popped and previous is known',
+      () {
+    fakeAsync((async) {
+      observer.didPop(route, previousRoute);
+
+      async.elapse(const Duration(milliseconds: 1000));
+
+      verify(
+        mScreenLoadingManager.startUiTrace(previousScreen),
+      ).called(1);
+
+      verify(
+        mHost.reportScreenChange(previousScreen),
+      ).called(1);
+    });
+  });
+
+  test(
+      'should not report screen change when a route is popped and previous is not known',
+      () {
+    fakeAsync((async) {
+      observer.didPop(route, null);
+
+      async.elapse(const Duration(milliseconds: 1000));
+
+      verifyNever(
+        mScreenLoadingManager.startUiTrace(any),
+      );
+
+      verifyNever(
+        mHost.reportScreenChange(any),
+      );
+    });
+  });
+}
+
+Route createRoute(String? name) {
+  return MaterialPageRoute(
+    builder: (_) => Container(),
+    settings: RouteSettings(name: name),
+  );
+}