在玩笑中编写单元测试时预期会出现特定错误

Question

我使用 nestjs (6.5.0) 和 jest (24.8) 并有一个抛出错误的方法：

  public async doSomething(): Promise<{ data: string, error?: string }> {
    throw new BadRequestException({ data: '', error: 'foo' });
  }

如何编写单元测试来检查我们是否获得了预期数据的预期异常？显而易见的解决方案是：

it('test', async () => {
  expect(await userController.doSomething())
    .rejects.toThrowError(new BadRequestException({ data: '', error: 'foo'});
});

但这不起作用，因为new BadRequestException()创建了一个具有不同调用堆栈的对象。我该如何测试？

Answer 1

与jest 文档中的示例相比，您在这里可能有 2 个问题。

• await应该在expect论点之外
• rejects 意味着抛出了一个错误，所以你测试是否相等

就像是：

it('test', async () => {
  await expect(userController.doSomething())
    .rejects.toEqual(new BadRequestException({ data: '', error: 'foo'});
});

Answer 2

回答我自己的问题：

使用自定义匹配器（见下文），测试可以编写为：

it('test', async () => {
  await expect(userController.doSomething()).rejects.toContainException(
    new BadRequestException({ data: '', error: 'foo' }),
  );
});

自定义匹配器：

import { HttpException } from '@nestjs/common';

// ensure this is parsed as a module.
export {};

// https://stackoverflow.com/questions/43667085/extending-third-party-module-that-is-globally-exposed

declare global {
  namespace jest {
    interface Matchers<R> {
      toContainException: (expected: R | any) => {};
    }
  }
}

// this will extend the expect with a custom matcher
expect.extend({
  toContainException<T extends HttpException>(received: T, expected: T) {
    const success =
      this.equals(received.message, expected.message) &&
      this.equals(received.getStatus(), expected.getStatus());

    const not = success ? ' not' : '';
    return {
      message: () =>
        `expected Exception ${received.name}${not} to be ${expected.name}` +
        '\n\n' +
        `Expected: ${this.utils.printExpected(expected.message)}, ` +
        `status: ${this.utils.printExpected(expected.getStatus())} \n` +
        `Received: ${this.utils.printReceived(received.message)}, ` +
        `status: ${this.utils.printReceived(received.getStatus())}`,
      pass: success,
    };
  },
});