Integrate logging system into Flutter app with service registration and testing setup

finlog_app/fluttery/test/fluttery_test.dart

@@ -1,12 +1,37 @@
-import 'package:flutter_test/flutter_test.dart';
-
 import 'package:fluttery/fluttery.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fluttery/logger/logger.dart';
+import 'package:fluttery/src/logger/logger_impl.dart';
+import 'package:kiwi/kiwi.dart';
+
+import 'mocks/mocks.dart';
 
 void main() {
-  test('adds one to input values', () {
-    final calculator = Calculator();
-    expect(calculator.addOne(2), 3);
-    expect(calculator.addOne(-7), -6);
-    expect(calculator.addOne(0), 1);
+  group('App Service Tests', () {
+    // Clear the singleton state before each test to ensure isolation
+    setUp(() {
+      // KiwiContainer provides a clear method to remove all registered services
+      KiwiContainer().clear();
+    });
+
+    test('should register and resolve a custom service', () {
+      // Register a mock logger service
+      final mockLogger = MockLogger();
+      App.registerService<Logger>(() => mockLogger);
+
+      // Resolve the service and check if it's the same instance
+      final resolvedLogger = App.service<Logger>();
+      expect(resolvedLogger, isA<MockLogger>());
+      expect(resolvedLogger, same(mockLogger));
+    });
+
+    test('should register and resolve default services', () {
+      // Register default services
+      App.registerDefaultServices();
+
+      // Resolve the Logger service and check if it's an instance of LoggerImpl
+      final logger = App.service<Logger>();
+      expect(logger, isA<LoggerImpl>());
+    });
   });
 }