Hi all, I’ve previously written pact tests using axios as the http handler but the consumer app itself uses fetch (from node-fetch) instead. I’ve tried to switch to using fetch but hit problems. I understand that using jest-pact is a possible solution so I’ve implemented the following example:

import { URL } from 'url';

import { Matchers } from '@pact-foundation/pact';
import { HTTPMethod } from '@pact-foundation/pact/src/common/request';
import { pactWith } from 'jest-pact';
import fetch from 'node-fetch';

jest.setTimeout(30000);

pactWith({ consumer: 'aggregator', provider: 'theme_provider' }, (provider) => {
    describe('Theme related end points', () => {
        it('Request to save themes', async () => {
            const url = new URL(`${provider.mockService.baseUrl}/themes-service/themes`);

            const { validateExample } = Matchers;

            const interaction = {
                state: 'Request to save themes',
                uponReceiving: 'Request to save themes',
                withRequest: {
                    method: <http://HTTPMethod.POST|HTTPMethod.POST>,
                    path: url.pathname,

                    headers: { Accept: 'application/json' },
                },
                willRespondWith: {
                    status: 200,
                    headers: { 'Content-Type': 'application/json' },
                    body: {
                        results: [{ handle: 'abc', result: 'Created' }],
                    },
                },
            };

            await provider.addInteraction(interaction);
            const result = await fetch(`${provider.mockService.baseUrl}/themes-service/themes`, {
                method: <http://HTTPMethod.POST|HTTPMethod.POST>,
                headers: {
                    Accept: 'application/json',
                    'Content-Type': 'application/json',
                },
            });

            expect(await result.json()).toEqual({
                results: [
                    {
                        handle: 'abc',
                        result: 'Created',
                    },
                ],
            });
        });
    });
});

Unfortunately, I get the following error:

FAIL  __pact__/fetch2.pact.spec.ts (10.793 s)
  Pact between aggregator and theme_provider
    with 30000 ms timeout for Pact
      Theme related end points
        ✕ Request to save themes (59 ms)

  ● Pact between aggregator and theme_provider › with 30000 ms timeout for Pact › Theme related end points › Request to save themes

    FetchError: invalid json response body at  reason: Unexpected end of JSON input

      42 |             });
      43 |
    > 44 |             expect(await result.json()).toEqual({
         |                    ^
      45 |                 results: [
      46 |                     {
      47 |                         handle: 'abc',

      at node_modules/cross-fetch/node_modules/node-fetch/lib/index.js:273:32
      at Object.<anonymous> (__pact__/fetch2.pact.spec.ts:44:20)

If I remove

await

from the offending line of code then the test fails because the response promise never gets fulfilled 😕

FAIL  __pact__/fetch2.pact.spec.ts (12.368 s)
  Pact between aggregator and theme_provider
    with 30000 ms timeout for Pact
      Theme related end points
        ✕ Request to save themes (65 ms)

  ● Pact between aggregator and theme_provider › with 30000 ms timeout for Pact › Theme related end points › Request to save themes

    expect(received).toEqual(expected) // deep equality

    - Expected  - 8
    + Received  + 1

    - Object {
    -   "results": Array [
    -     Object {
    -       "handle": "abc",
    -       "result": "Created",
    -     },
    -   ],
    - }
    + Promise {}

      42 |             });
      43 |
    > 44 |             expect(result.json()).toEqual({
         |                                   ^
      45 |                 results: [
      46 |                     {
      47 |                         handle: 'abc',

      at Object.<anonymous> (__pact__/fetch2.pact.spec.ts:44:35)

What am I missing or overlooking? I'd be really grateful for any assistance on this problem 🙂

What do the mock server logs say they received?

Hi Matt, not sure where to find the logs for the mock server.

That error is pretty clear - the fetch call didn't send the request to the expected path. My guess is it's something to do with running fetching in a node process

Hi @Matt (pactflow.io / pact-js / pact-go), is this a known issue between pact-js and fetch? Any other advice on how to proceed with this issue?

I'm not aware of any issues

Hi @Matt (pactflow.io / pact-js / pact-go) Looks like we got to the bottom of our problem with using fetch and pact-js.

Ha, yes that'll do it 🤣