I am currently using node-fetch and nock for an express server that sits on top of an angular project.

I have the following middleware that is making a call to an api:

export const middleware = async(response: any) => {
    try {
        const result = await fetch(url).then(res => res.json())
        return response.status(200).json(result);
    } catch(err) {
        logger.error({eventId: 'get-content', err});
        return response.status(500)
    }
}

and my test is as follows:

describe('API service', () => {
    let response, scope;
    beforeEach(() => {
        response = {
            status(s) { this.statusCode = s; return this; },
            json(result) { this.res = result; return this; },
        };
    })

    afterEach(() => {
        nock.restore();
    })

    it('should return a 200 response from successful call api', (done) => {
        scope = nock(url)
            .get(/.*/)
            .reply(200, {data: 'content'})

        middleware(response).then(data => {
            expect(response.status).toEqual(200);
            expect(response.data).toEqual('content');
            scope.isDone();
            done();
        })
    })
})

However, nock is not mocking the data response from the middleware function. Instead, I'd have to use scope to access its parameters.

The middleware function acts as if nock never mocked its response. Why is this occurring? Am I missing a configuration?

I am serving my tests using karma runner.

I am currently using node-fetch and nock for an express server that sits on top of an angular project.

I have the following middleware that is making a call to an api:

export const middleware = async(response: any) => {
    try {
        const result = await fetch(url).then(res => res.json())
        return response.status(200).json(result);
    } catch(err) {
        logger.error({eventId: 'get-content', err});
        return response.status(500)
    }
}

and my test is as follows:

describe('API service', () => {
    let response, scope;
    beforeEach(() => {
        response = {
            status(s) { this.statusCode = s; return this; },
            json(result) { this.res = result; return this; },
        };
    })

    afterEach(() => {
        nock.restore();
    })

    it('should return a 200 response from successful call api', (done) => {
        scope = nock(url)
            .get(/.*/)
            .reply(200, {data: 'content'})

        middleware(response).then(data => {
            expect(response.status).toEqual(200);
            expect(response.data).toEqual('content');
            scope.isDone();
            done();
        })
    })
})

However, nock is not mocking the data response from the middleware function. Instead, I'd have to use scope to access its parameters.

The middleware function acts as if nock never mocked its response. Why is this occurring? Am I missing a configuration?

I am serving my tests using karma runner.

• javascript
• node.js
• unit-testing
• testing
• karma-jasmine

2 Answers 2

Nock works by overriding Node's http.request function. Also, it overrides http.ClientRequest too to cover for modules that use it directly.

• https://github./nock/nock#how-does-it-work

Unfortunately it appears fetch does not make use of the http.request or http.ClientRequest meaning the requests are never intercepted by nock.

A better approach may be to mock fetch with a library such as fetch-mock.

I have tried the same & it is working fine for me. Can you check the below piece of code & try.

const fetch = require('node-fetch');
const nock = require('nock');

describe('My Fetch POST Test with Nock', () => {
  it('should mock a POST fetch call using nock', async () => {
    // Set up the nock mock for the URL and the POST request
    const requestBody = { key: 'value' };
    const scope = nock('https://api.example.')
      .post('/data', requestBody)
      .reply(201, { message: 'Created successfully' });

    // Perform the fetch call
    const response = await fetch('https://api.example./data', {
      method: 'POST',
      body: JSON.stringify(requestBody),
      headers: {
        'Content-Type': 'application/json',
      },
    });
    const data = await response.json();

    // Ensure all expectations of the nock mock are satisfied
    scope.done();
  });
});