work on test models part 1

test/model/error_test.dart

@@ -0,0 +1,84 @@
+////////////////////////////
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tm_app/data/services/model/error/error_model.dart';
+
+void main() {
+  group('ErrorModel Tests', () {
+    test('fromJson should parse JSON correctly', () {
+      final json = {
+        'message': 'Invalid request',
+        'code': '400',
+        'details': 'Missing required field: email',
+      };
+
+      final error = ErrorModel.fromJson(json);
+
+      expect(error.message, 'Invalid request');
+      expect(error.code, '400');
+      expect(error.details, 'Missing required field: email');
+    });
+
+    test('toJson should return valid JSON map', () {
+      const error = ErrorModel(
+        message: 'Unauthorized',
+        code: '401',
+        details: 'Token expired',
+      );
+
+      final json = error.toJson();
+
+      expect(json, isA<Map<String, dynamic>>());
+      expect(json['message'], 'Unauthorized');
+      expect(json['code'], '401');
+      expect(json['details'], 'Token expired');
+    });
+
+    test(' copyWith should modify specific fields only', () {
+      const error = ErrorModel(
+        message: 'Something went wrong',
+        code: '500',
+        details: 'Server error',
+      );
+
+      final updated = error.copyWith(
+        message: 'Timeout error',
+      );
+
+      expect(updated.message, 'Timeout error');
+      expect(updated.code, '500');
+      expect(updated.details, 'Server error');
+    });
+
+    test('fromJson handles null fields safely', () {
+      final json = {
+        'message': null,
+        'code': null,
+        'details': null,
+      };
+
+      final error = ErrorModel.fromJson(json);
+
+      expect(error.message, isNull);
+      expect(error.code, isNull);
+      expect(error.details, isNull);
+    });
+
+    test('fromJson -> toJson round-trip should preserve data', () {
+      final json = {
+        'message': 'Not Found',
+        'code': '404',
+        'details': 'User not found',
+      };
+
+      final error = ErrorModel.fromJson(json);
+      final output = error.toJson();
+
+      expect(output['message'], 'Not Found');
+      expect(output['code'], '404');
+      expect(output['details'], 'User not found');
+    });
+  });
+}
+
+////////////////////////////