fix: fix null safety issues and tests (#2)

Author: jeroen-meijer

lib/mock_navigator.dart

@@ -4,7 +4,6 @@ library mock_navigator;
 
 import 'package:flutter/material.dart';
 import 'package:mocktail/mocktail.dart' as mocktail;
-import 'package:mockito/mockito.dart' as mockito;
 
 /// A template fake route, useful for registering fallbacks when using the
 /// `mocktail` package.

pubspec.yaml

@@ -11,11 +11,10 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  mockito: 4.1.3
-  mocktail: 0.1.1
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
   coverage: 0.15.2
+  mocktail: 0.1.1
   very_good_analysis: 2.0.3

test/mock_navigator_test.dart

@@ -4,6 +4,10 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:mock_navigator/mock_navigator.dart';
 import 'package:mocktail/mocktail.dart';
 
+class MockNavigator extends Mock
+    with MockNavigatorDiagnosticsMixin
+    implements MockNavigatorBase {}
+
 extension on WidgetTester {
   Future<void> pumpTest(Widget widget) async {
     await pumpWidget(
@@ -19,14 +23,14 @@ extension on WidgetTester {
 
 void main() {
   group('MockNavigator', () {
-    late MockNavigator navigator;
+    late MockNavigatorBase navigator;
 
     setUpAll(() {
       registerFallbackValue<Route<Object?>>(FakeRoute<Object?>());
     });
 
     setUp(() {
-      navigator = MocktailNavigator();
+      navigator = MockNavigator();
     });
 
     testWidgets('mocks .push calls', (tester) async {