added UserTokenService spec

src/common/user/token/user-token.service.spec.ts

+import { UserTokenService } from './user-token.service';
+import { UserToken } from './user-token';
+
+describe('UserTokenService', () => {
+  let service: UserTokenService;
+
+  beforeEach(() => {
+    service = new UserTokenService();
+  });
+
+  describe('generate', () => {
+    it('should return UserToken', () => {
+      const fakeUser = {
+        email: 'fake@localh.ost',
+        password: '123456',
+        verify: async (password: string) => true,
+      };
+      expect(service.generate(fakeUser)).resolves.toBeInstanceOf(UserToken);
+    });
+  });
+});