Mock http requests made using fetch (or isomorphic-fetch). As well as shorthand methods for the simplest use cases, it offers a flexible API for customising mocking behaviour, and can also be persisted (with resettable state) over a series of tests.

• Browser tests: require('fetch-mock)
• Server side tests running in nodejs 4 or higher: require('fetch-mock/server')
• Server side tests running in nodejs 0.12 or lower: require('fetch-mock/es5/server)

You will need to ensure fetch and Promise are already available as globals in your environment

To output useful messages for debugging export DEBUG=fetch-mock

require('fetch-mock') exports a singleton with the following methods

Replaces fetch() with a stub which records it's calls, grouped by route, and optionally returns a stub response or passes the call through to fetch().

• mock(matcher, response) - configuration for a single unnamed route to be mocked (shorthand for mock(route) - see below)

• mock(matcher, method, response) - configuration for a single unnamed route to be mocked for a given method (shorthand for mock(route) - see below)

• mock(route) - configuration for a single route with the following properties

  • name [required]: A unique string naming the route
  • method [optional]: If specified will only match requests using the given http method
  • matcher [required]: The rule for matching calls to fetch(). Accepts any of the following
    • string: Either an exact url to match e.g. 'http://www.site.com/page.html' or, if the string begins with a ^, the string following the ^ must begin the url e.g. '^http://www.site.com' would match 'http://www.site.com' or 'http://www.site.com/page.html'
    • RegExp: A regular expression to test the url against
    • Function(url, opts): A function (returning a Boolean) that is passed the url and opts fetch() is called with.
  • response [required]: Configures the response object returned by the mock. Can take any of the following values
    • number: Creates a response with this status
    • string: Creates a 200 response with the string as the response body
    • object: As long as the object does not contain any of the properties below it is converted into a json string and returned as the body of a 200 response. If any of the properties below are defined it is used to configure a Response object
      • body: Set the response body (string or object)
      • status: Set the response status (defaut 200)
      • headers: Set the response headers. (object)
      • throws: If this property is present then a Promise rejected with the value of throws is returned
    • Function(url, opts): A function that is passed the url and opts fetch() is called with and that returns any of the responses listed above

• mock(routes) - array of route configuration objects (see above)

• mock(config) - object containing more complex config for fine grained controlled over mocking behaviour with the following properties

  • routes: Either a single route config object or an array of them (see above)
  • responses: When registerRoute() has already been used to register some routes then responses can be used to override the default response. Its value should be an object mapping route names to responses, which should be similar to those provided in the response property of stanadard route configurations e.g.

     responses: {
     	session: function (url, opts) {
     		if (opts.headers.authorized) {
     			return {user: 'dummy-authorized-user'};
     		} else {
     			return {user: 'dummy-unauthorized-user'};
     		}
     	}
     }

  • greed: Determines how the mock handles unmatched requests
    • 'none': all unmatched calls get passed through to fetch()
    • 'bad': all unmatched calls result in a rejected promise
    • 'good': all unmatched calls result in a resolved promise with a 200 status

Restores fetch() to its unstubbed state and clears all data recorded for its calls

Normally calling mock() twice without restoring inbetween will throw an error. reMock() calls restore() internally before calling mock() again. This allows you to put a generic call to mock() in a beforeEach() while retaining the flexibility to vary the responses for some tests

Clears all data recorded for fetch()'s calls

Returns an array of arrays of the arguments passed to fetch() that matched the given route. '__unmatched' can be passed in to return results for calls not matching any route.

When shorthands are used by mock() to define unnamed routes routeName is not required (but _mock can be passed in to distinguish from calls to previously registered routes)

Returns a Boolean denoting whether any calls matched the given route. '__unmatched' can be passed in to return results for calls not matching any route. If no routeName is passed it returns true if any fetch calls were made

Often your application/module will need a mocked response for some http requests in order to initialise properly, even if the content of those calls are not the subject of a given test e.g. a mock response from an authentication service and a multi-variant testing service might be necessary in order to test the UI for a version of a log in form. It's helpful to be able to define some default responses for these services which will exist throughout all or a large subset of your tests. registerRoute() aims to fulfil this need. All these predefined routes can be overridden when mock(config) is called.

• registerRoute(object): An object similar to the route objects accepted by mock()
• registerRoute(array): An array of the above objects
• registerRoute(name, matcher, response): The 3 properties of the route object spread across 3 parameters

Unregisters one or more previously registered routes. Accepts either a string or an array of strings

When using isomorphic-fetch or node-fetch ideally fetch should be added as a global. If not possible to do so you can still use fetch-mock in combination with mockery in nodejs. To use fetch-mock with with mockery you will need to use this function to prevent fetch-mock trying to mock the function globally.

• func Optional reference to fetch (or any other function you may want to substitute for fetch in your tests).

var fetch = require('node-fetch');
var fetchMock = require('fetch-mock');
var mockery = require('mockery');
fetchMock.useNonGlobalFetch(fetch);

fetchMock.registerRoute([
 ...
])
it('should make a request', function (done) {
	mockery.registerMock('fetch', fetchMock.mock());
	// test code goes in here
	mockery.deregisterMock('fetch');
	done();
});

var fetchMock = require('fetch-mock');

// Simplest use case
it('should pretend to be Rambo', done => {
	fetchMock.mock('http://rambo.was.ere', 301);
	fetch('http://rambo.was.ere')
		.then(res => {
			expect(fetchMock.calls().length).to.equal(1);
			expect(res.status).to.equal(301);
			fetchMock.restore();
			done();
		});
})

// Optionally set up some routes you will always want to mock
// Accepts an array of config objects or three parameters,
// name, matcher and response, to add a single route
fetchMock.registerRoute([
 {
	 name: 'session',
	 matcher: 'https://sessionservice.host.com',
	 response: {
	 	body: 'user-12345',
	 	// opts is as expected by https://github.com/bitinn/node-fetch/blob/master/lib/response.js
	 	// headers should be passed as an object literal (fetch-mock will convert it into a Headers instance)
	 	// status defaults to 200
	 	opts: {
	 		headers: {
	 			'x-status': 'unsubscribed'
	 		},
	 		status: 401
	 	}
	 }
 },
 {
	name: 'geo',
	matcher: /^https\:\/\/geoservice\.host\.com/,
	// objects will be converted to strings using JSON.stringify before being returned
	response: {
	 	body: {
			country: 'uk'
		}
	}
 }
])


it('should do A', function () {
	fetchMock.mock({
		// none: all unmatched calls get sent straight through to the default fetch
		// bad: all unmatched calls result in a rejected promise
		// good: all unmatched calls result in a resolved promise with a 200 status
		greed: 'none'
	});

	thingToTest.exec();

	// returns an array of calls to the session service,
	// each item in the array is an array of the arguments passed to fetch
	// similar to sinon.spy.args
	fetchMock.calls('session') // non empty array
	fetchMock.called('geo') // Boolean

	// reset all call logs
	fetchMock.reset()

	fetchMock.calls('session') // undefined
	fetchMock.called('geo') // false

	// fetch itself is just an ordinary sinon.stub
	fetch.calledWith('thing')

	// restores fetch and resets all data
	fetchMock.restore();
})

describe('content', function () {
	before(function () {
		// register an additional route, this one has a more complex matching rule
		fetchMock.registerRoute('content', function (url, opts) {
			return opts.headers.get('x-api-key') && url.test(/^https\:\/\/contentservice\.host\.com/);
		}, {body: 'I am an article'});
	});

	after(function () {
		fetchMock.unregisterRoute('content');
	})

	it('should do B', function () {


		fetchMock.mock({
			// you can choose to mock a subset of the registered routes
			// and even add one to be mocked for this test only
			// - the route will exist until fetchMock.restore() is called
			routes: ['session', 'content', {
			 name: 'enhanced-content',
			 matcher: /^https\:\/\/enhanced-contentservice\.host\.com/,
			 // responses can be contextual depending on the request
			 // url and opts parameters are exactly what would be passed to fetch
			 response: function (url, opts) {
				return {body: 'enhanced-article-' + url.split('article-id/')[1]};
			 }
			}]
		});

		thingToTest.exec();

		fetchMock.calls('content') // non empty array
		fetchMock.called('enhanced-content') // Boolean

		// restores fetch and resets all data
		fetchMock.restore();
	})

	it('should do C', function () {


		fetchMock.mock({
			// you can override the response for a service for this test only
			// this means e.g. you can configure an authentication service to return
			// a valid user normally, but only return invalid for the one test
			// where you're testing authentication
			responses: {
				'session': 'invalid-user'
			}
		});

		thingToTest.exec();

		// restores fetch and resets all data
		fetchMock.restore();
	})

});