如何测试 Nestjs 拦截器？

Question

我找不到任何关于如何在 NestJS 中测试拦截器的解释

这个简单的例子截取了一个 POST 查询以向正文中提供的示例模型添加一个属性。

@Injectable()
export class SubscriberInterceptor implements NestInterceptor {
  async intercept(
    context: ExecutionContext,
    next: CallHandler,
  ): Promise<Observable<ExampleModel>> {
    let body: ExampleModel = context.switchToHttp().getRequest().body;
    body = {
      ...body,
      addedAttribute: 'example',
    };
    context.switchToHttp().getRequest().body = body;
    return next.handle();
  }
}

我想测试拦截函数中发生了什么。

到目前为止：

const interceptor = new SubscriberInterceptor();

describe('SubscriberInterceptor', () => {
  it('should be defined', () => {
    expect(interceptor).toBeDefined();
  });

  describe('#intercept', () => {
    it('should add the addedAttribute to the body', async () => {
      expect(await interceptor.intercept(arg1, arg2)).toBe({ ...bodyMock, addedAttribute: 'example' });
    });
  });
});

我的问题：我应该只模拟 arg1: ExecutionContext 和 arg2: CallHandler 吗？如果是这样，如何模拟arg1 和arg2？否则我应该如何进行？

Answer 1

你是对的，你应该模拟arg1和arg2，然后将它们传递给intercept方法，这里是解决方案：

SubscriberInterceptor.ts:

interface ExecutionContext {
  switchToHttp(): any;
}
interface CallHandler {
  handle(): any;
}
interface Observable<T> {}
interface ExampleModel {}

interface NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Promise<Observable<ExampleModel>>;
}

export class SubscriberInterceptor implements NestInterceptor {
  public async intercept(context: ExecutionContext, next: CallHandler): Promise<Observable<ExampleModel>> {
    let body: ExampleModel = context.switchToHttp().getRequest().body;
    body = {
      ...body,
      addedAttribute: 'example'
    };
    context.switchToHttp().getRequest().body = body;
    return next.handle();
  }
}

单元测试，executionContext的模拟链式方法

import { SubscriberInterceptor } from './';

const interceptor = new SubscriberInterceptor();

const executionContext = {
  switchToHttp: jest.fn().mockReturnThis(),
  getRequest: jest.fn().mockReturnThis()
};

const callHandler = {
  handle: jest.fn()
};

describe('SubscriberInterceptor', () => {
  it('should be defined', () => {
    expect(interceptor).toBeDefined();
  });
  describe('#intercept', () => {
    it('t1', async () => {
      (executionContext.switchToHttp().getRequest as jest.Mock<any, any>).mockReturnValueOnce({
        body: { data: 'mocked data' }
      });
      callHandler.handle.mockResolvedValueOnce('next handle');
      const actualValue = await interceptor.intercept(executionContext, callHandler);
      expect(actualValue).toBe('next handle');
      expect(executionContext.switchToHttp().getRequest().body).toEqual({
        data: 'mocked data',
        addedAttribute: 'example'
      });
      expect(callHandler.handle).toBeCalledTimes(1);
    });
  });
});

单元测试结果：

 PASS  src/mock-function/57730120/index.spec.ts
  SubscriberInterceptor
    ✓ should be defined (10ms)
    #intercept
      ✓ t1 (11ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        1.235s, estimated 3s