added a dedicated error handler service

src/error-message/error-message.service.spec.ts

@@ -0,0 +1,18 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { ErrorMessageService } from './error-message.service';
+
+describe('ErrorMessageService', () => {
+  let service: ErrorMessageService;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      providers: [ErrorMessageService],
+    }).compile();
+
+    service = module.get<ErrorMessageService>(ErrorMessageService);
+  });
+
+  it('should be defined', () => {
+    expect(service).toBeDefined();
+  });
+});