api.js

import request from 'superagent';

export const getWeatherForCity = (city, country) => {
  return new Promise((resolve, reject) => {
    request
      .get('http://api.openweathermap.org/data/2.5/weather')
      .query({
        q: `${city},${country}`,
        units: 'metric',
        APPID: 'ABC123'
      })
      .end((err, res) => {
        if (err) { reject (err)      }
        else     { resolve(res.body) }
      })
  })
}

mocks.js

// ./superagent-mock-config.js file

const cityResponse = {
    "coord": {
        "lon": 13.41,
        "lat": 52.52
    },
    "weather": [
        {
            "id": 800,
            "main": "Clear",
            "description": "clear sky",
            "icon": "01d"
        }
    ],
    "base": "stations",
    "main": {
        "temp": 17,
        "pressure": 1026,
        "humidity": 67,
        "temp_min": 17,
        "temp_max": 17
    },
    "visibility": 10000,
    "wind": {
        "speed": 4.1,
        "deg": 100
    },
    "clouds": {
        "all": 0
    },
    "dt": 1506594000,
    "sys": {
        "type": 1,
        "id": 4892,
        "message": 0.0021,
        "country": "DE",
        "sunrise": 1506574995,
        "sunset": 1506617363
    },
    "id": 2950159,
    "name": "Berlin",
    "cod": 200
}

const rules = [
  {
    pattern: 'http://api.openweathermap.org/data/2.5/weather(.*)',

    fixtures: function (match, params, headers, context) {
      // City search: success
      if (match[1] === '?q=Berlin%2CDE&units=metric&APPID=ABC123') {
        return cityResponse
      }

      // City search: failure
      if (match[1] === '?q=Foo%2CBar&units=metric&APPID=ABC123') {
        throw new Error(500);
      }    
    },
    
    get: function (match, data) {
      return {
        body: data
      };
    }
  }
];

module.exports = {
  cityResponse: cityResponse,
  rules: rules
}

tests.js

import { getWeatherForGeoloc, getWeatherForCity } from 'api'

import request from 'superagent';
import * as apiMocks from 'mocks'

describe('API', () => {
  var mock = null
  beforeEach(() => mock = require('superagent-mock')(request, apiMocks.rules))
  afterEach(() => mock.unset())

  describe('#getWeatherForCity', () => {
    it('should process success result', () => {
      getWeatherForCity('Berlin', 'DE').then(body => {
        expect(body).toEqual(apiMocks.cityResponse)
      })
    })

    it('should process failure result', () => {
      getWeatherForCity('Foo', 'Bar').then(() => {},
        err => expect(err).toEqual(Error(500))
      )
    })
  })
})