CODEWITHSUNDEEP
javascriptnode.jsjestjses6-promise
QuickLearner
QuickLearner

Reputation: 345

How to handle the Promise rejects in the test cases in Jest?

I am working on a node JS project for which I am writing test cases. Code -

jest.mock('../../utils/db2.js')
const request = require('supertest')
const executeDb2Query = require('../../utils/db2.js')
const app = require('../../app')

describe('check connect test', () => {
  beforeEach(() => {
    jest.resetModules()
  })

  it('check Bad Pool', async () => {
    executeDb2Query.mockImplementation(() =>
      Promise.reject(new Error('Unable to connect to db2'))
    )
    const response = await request(app).get(
      '/api/v1/abc/xyz/123456'
    )
    expect(response).rejects.toMatch('Unable to connect to db2')

    //expect(response.body.msg).toEqual('Unable to connect to db2')
    expect(response.status).toEqual(500)
  })

executeDb2query is a method which executes the query. The commented line is working fine but when I add rejects.toMatch , the test case fails saying below -

check connect test › check Bad Pool

    expect(received).rejects.toMatch()

    Matcher error: received value must be a promise or a function returning a promise

    Received has type:  object
    Received has value: {"header": {"connection": "close", "content-length": "2", "content-security-policy-report-only"

  )
    > 24 |     expect(response).rejects.toMatch('Unable to connect to db2')
         |                              ^
      25 |
      26 |     //expect(response.body.msg).toEqual('Unable to connect to db2')
      27 |     expect(response.status).toEqual(500)

      at Object.toMatch (node_modules/expect/build/index.js:226:11)

For resolves case -

it('check Good Pool', () => {
    executeDb2Query.mockImplementation(() =>
      Promise.resolve([
        {
          isAvailable: true
        }
      ])
    )
    const response = request(app).get('/api/v1/abc/xyz/090703')
    expect(response).resolves.toStrictEqual([
      {
        isAvailable: true
      }
    ])
  })

Error -

 expect(received).resolves.toStrictEqual()

    Matcher error: received value must be a promise

    Received has value: undefined

      35 |     )
      36 |     const response = request(app).get('/api/v1/abc/xyz/090703')
    > 37 |     expect(response.body).resolves.toStrictEqual([
         |                                    ^
      38 |       {
      39 |         isAvailable: true
      40 |       }

      at Object.toStrictEqual (node_modules/expect/build/index.js:185:11)

On further checking, test cases are passing but giving out errors -

(node:23978) UnhandledPromiseRejectionWarning: Error: expect(received).rejects.toThrow()

Received promise resolved instead of rejected
Resolved to value: {"header": {"connection": "close", "content-length": "1499", "content-security-policy-report-only"

(node:23978) UnhandledPromiseRejectionWarning: Error: expect(received).resolves.toStrictEqual(expected) // deep equality

Expected: [{"isAvailable": true}]
Received: {"header": {"connection": "close", "content-length": "1499", "content-security-policy-report-only": "default-src 'self'"

I tried searching online and tried various things but keep getting the same error.

Any suggestions?

Upvotes: 1

Views: 8047

Answers (1)

Robert Kawecki
Robert Kawecki

Reputation: 2448

expect(response).rejects assumes response to be a Promise. However, you're already using await, so response is not a Promise - it is the resolution value of that promise.
Remove the await, or (if you're getting a response rather than a promise rejection) keep the await but stop matching on .rejects.

If you decide to keep using expect(...).rejects, you may need to await the assertion:

await expect(...).rejects.toMatch(...);

Upvotes: 5

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