Nock not intercepting http requests

Question

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.

Answer 1

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.com/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.