The presence of 'eventually' in the Chai Mocha test Promise Property is undefined

I'm having trouble with using Chai Promise test in a Docker environment.

Here is a simple function:


    let funcPromise = (n) => {
        return new Promise((resolve, reject) =>{
            if(n=="a") {
                resolve("success");
            } else {
                reject("Fail");
            }
        });
    }

A simple test:


    import chai from 'chai';
    var chaiAsPromised = require('chai-as-promised');
    chai.use(chaiAsPromised);
    let expect = chai.expect;
    let assert = chai.assert;               

    it('connect: test promise', (done) => {
        let func = funcPromise("a");
        expect(func).to.eventually.equal("success"); // not working
        expect(func).to.be.rejected; // not working
    })

Error displayed on the terminal: 

FileTest.spec.ts:43:25 - error TS2339: Property 'eventually' does not exist on type 'Assertion'.

storage/database/MongooseEngine.spec.ts:44:35 - error TS2339: Property 'rejected' does not exist on type 'Assertion'.

typescriptunit-testingmocha.jschai

Answer №1

The issue arises from TypeScript not recognizing the extensions that chai-as-promised introduces to the chai assertions.

To resolve this, simply include the type definitions for chai-as-promised:

npm install --save-dev @types/chai-as-promised

Additionally, remember to use await when handling assertions with chai-as-promised:

import chai from 'chai';
import chaiAsPromised from 'chai-as-promised';
chai.use(chaiAsPromised);
const expect = chai.expect;

const funcPromise = (n) => new Promise((resolve, reject) => {
  if (n === 'a') { resolve('success'); }
  else { reject('fail'); }
});

it('check: test promise', async () => {
  await expect(funcPromise('a')).to.eventually.equal('success');  // Successful!
  await expect(funcPromise('b')).to.be.rejected;  // Success!
});

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