Chai 没有使用 async/await 捕获抛出的错误

Question

Because a promise is returned Chai doesnt catch the exception, how can I resolve this?

Here is my test.

describe('test.js', function() {
    it('Ensures throwError() throws error if no parameter is supplied.', async function() {
        expect(async function() {
            const instance = new Class();
            await instance.throwError();
        }).to.throw(Error);
    });
});

Here is my code.

class Class{
    async throwError(parameter) {
        try {
            if (!parameter) {
                throw Error('parameter required');
            }
        } catch (err) {
            console.log(err);
        }
    }
}

The message from Chai.

AssertionError: expected [Function] to throw Error

But I can see this message on the call stack.

(node:21792) UnhandledPromiseRejectionWarning: Error: Error: parameter required

Answer 1

expect().to.throw() only support sync function. For async function, you need to use chai-as-promised .

Eg

index.js :

export class Class {
  async throwError(parameter) {
    if (!parameter) {
      throw Error('parameter required');
    }
  }
}

index.test.js :

import chai, { expect } from 'chai';
import chaiAsPromised from 'chai-as-promised';
import { Class } from '.';

chai.use(chaiAsPromised);

describe('62596956', function() {
  it('Ensures throwError() throws error if no parameter is supplied.', async function() {
    const instance = new Class();
    await expect(instance.throwError(null)).to.eventually.rejectedWith(Error);
  });
});

unit test result:

  62596956
    ✓ Ensures throwError() throws error if no parameter is supplied.


  1 passing (9ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |       50 |     100 |     100 |                   
 index.ts |     100 |       50 |     100 |     100 | 3                 
----------|---------|----------|---------|---------|-------------------