tests: add chat model tests(cv: 100)

test/dashbot/models/chat_message_model_test.dart

@@ -0,0 +1,65 @@
+import 'package:apidash/dashbot/core/constants/constants.dart';
+import 'package:apidash/dashbot/features/chat/models/chat_action.dart';
+import 'package:apidash/dashbot/features/chat/models/chat_message.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('ChatMessage equality & hashCode', () {
+    final ts = DateTime.utc(2025, 1, 2, 3, 4, 5);
+    const action = ChatAction(
+      action: 'update_field',
+      target: 'httpRequestModel',
+      field: 'url',
+      value: 'https://api.example.dev',
+      actionType: ChatActionType.updateField,
+      targetType: ChatActionTarget.httpRequestModel,
+    );
+
+    test('identical field values -> objects equal & same hashCode', () {
+      final msg1 = ChatMessage(
+        id: 'm1',
+        content: 'Hello',
+        role: MessageRole.user,
+        timestamp: ts,
+        messageType: ChatMessageType.general,
+        actions: const [action],
+      );
+      final msg2 = ChatMessage(
+        id: 'm1',
+        content: 'Hello',
+        role: MessageRole.user,
+        timestamp: ts,
+        messageType: ChatMessageType.general,
+        actions: const [action],
+      );
+      expect(msg1, msg2);
+      expect(msg1.hashCode, msg2.hashCode);
+      expect(msg1.toString(), contains('ChatMessage'));
+      expect(msg1.toString(), contains('m1'));
+    });
+
+    test('different id -> not equal', () {
+      final a = ChatMessage(
+        id: 'a',
+        content: 'Hi',
+        role: MessageRole.user,
+        timestamp: ts,
+      );
+      final b = a.copyWith(id: 'b');
+      expect(a == b, isFalse);
+    });
+
+    test('copyWith returns updated instance only for provided fields', () {
+      final base = ChatMessage(
+        id: 'base',
+        content: 'Original',
+        role: MessageRole.system,
+        timestamp: ts,
+      );
+      final updated = base.copyWith(content: 'Updated');
+      expect(updated.content, 'Updated');
+      expect(updated.id, 'base');
+      expect(updated.role, MessageRole.system);
+    });
+  });
+}