How to spyOn window.location.assign on Vuejs Application with Jest? - unit-testing

I am needing to spyOn window.location.assign for my unit test. But when I run the test I get this error.
Cannot spy the assign property because it is not a function; undefined given instead
Here is my code:
jest.spyOn(window.location, "assign");
Could anyone give me some hints or solutions on this case?

Since Jest v25 (Which uses a newer version of JSDOM) you will get the following error:
TypeError: Cannot assign to read only property 'assign' of object '[object Location]'
This is not a Jest/JSDOM bug by the way. This is normal browser behaviour and JSDOM tries to act like a real browser.
A workaround is to remove the location object, create your own one and after running your tests you should reset it to the original location object:
describe('My awesome unit test', () => {
// we need to save the original object for later to not affect tests from other files
const realLocation = global.location
beforeAll(() => {
delete global.location
global.location = { assign: jest.fn() }
// or even like this if you are also using other location properties (or if TypeScript complains):
// global.location = { ...realLocation, assign: jest.fn() }
})
afterAll(() => {
global.location = realLocation
})
it('should call location.assign', () => {
// ...your test code
expect(global.location.assign).toHaveBeenCalled()
// or even better:
// expect(global.location.assign).toHaveBeenCalledWith('/my_link')
})
})

As window can only be accessed through the global keyword in jest tests and window.location.assign is not implemented in jsdom, you can try
jest
.spyOn(global.location, "assign")
.mockImplementation(url => console.log(url))

Related

Stenciljs unit testing getting error : ReferenceError XMLHttpRequest is not defined

I'm trying to create units test for my stencil js component, in the compnentWillLoad() method it will do an HTTP request (using rxjs).when I'm run the test getting error ReferenceError: XMLHttpRequest is not defined.But when removing the HTTP request from the componentWillLoad() method test passed.
My test as below,
it('should render my component', async () => {
const page = await newSpecPage({
components: [MyComponent],
html: `<my-component></my-component>`,
});
expect(page.root).toEqualHtml(`<my-component></my-component>`);
});
I'm getting error ReferenceError: XMLHttpRequest is not defined
XMLHttpRequest is indeed not defined in the virtual DOM context that is created when you use newSpecPage.
The best solution for you is probably to write this as an E2E test instead, using newE2EPage, which is more suited for complete end-to-end testing because it runs in a real browser context where XMLHttpRequest will be available.
it('should render', async () => {
const page = await newE2EPage({ html: '<my-component></my-component>' });
const myComponent = page.find('my-component');
expect(myComponent).toHaveClass('hydrated');
});
"Spec Page" testing is rather meant for unit testing components that work stand-alone. If your goal is to actually unit-test your component and you just want to be able to instantiate your component but you don't actually need the request to succeed for testing, then you can also use the Build context from Stencil:
import { Build, ... } from '#stencil/core';
export class MyComponent {
componentWillLoad() {
if (!Build.isTesting) {
// make the request
}
}
// ...
}
I had similar troubles with Stencil, Jest and XMLHttpRequest.
First, make sure you call
new window.XMLHttpRequest()
instead of simply calling
new XMLHttpRequest()
This seems to be neccessary when using jsdom and may already resolve your issue.
It didn't resolve mine though, since I wanted to make sure there are no real API calls going on. So I tried to mock XMLHttpRequest. However, I ran into other issues while building the mock and finally decided to refactor my code to use Fetch API instead of XMLHttpRequest which seems to be better supported by Stencil.
You can easily mock fetch using jest
export function mockFetch(status, body, statusText?) {
// #ts-ignore
global.fetch = jest.fn(() =>
Promise.resolve({
status: status,
statusText: statusText,
text: () => Promise.resolve(JSON.stringify(body)),
json: () => Promise.resolve(body),
})
)
}

How to Test a Global Event Bus With Vue Test Utils?

I am trying to learn how to test events emitted through a global Event Bus. Here's the code with some comments in the places I don't know what to do.
// EvtBus.js
import Vue from 'vue';
export const EvtBus = new Vue();
<!-- CouponCode.vue -->
<template>
<div>
<input
class="coupon-code"
type="text"
v-model="code"
#input="validate">
<p v-if="valid">
Coupon Redeemed: {{ message }}
</p>
</div>
</template>
<script>
import { EvtBus } from '../EvtBus.js';
export default {
data () {
return {
code: '',
valid: false,
coupons: [
{
code: '50OFF',
discount: 50,
message: '50% Off!'
},
{
code: 'FREE',
discount: 100,
message: 'Entirely Free!'
}
]
};
},
created () {
EvtBus.$on('coupon-applied', () => {
//console.info('had a coupon applied event on component');
});
},
methods: {
validate () {
// Extract the coupon codes into an array and check if that array
// includes the typed in coupon code.
this.valid = this.coupons.map(coupon => coupon.code).includes(this.code);
if (this.valid) {
this.$emit('applied');
// I NEVER see this on the coupon-code.spec.js
EvtBus.$emit('coupon-applied');
}
}
},
computed: {
message () {
return this.coupons.find(coupon => coupon.code === this.code).message;
}
}
}
</script>
// tests/coupon-code.spec.js
import expect from 'expect';
import { mount } from '#vue/test-utils';
import CouponCode from '../src/components/CouponCode.vue';
import { EvtBus } from '../src/EvtBus.js';
describe('Reminders', () => {
let wrp;
beforeEach(() => {
wrp = mount(CouponCode);
});
it('broadcasts the percentage discount when a valid coupon code is applied', () => {
let code = wrp.find('input.coupon-code');
code.element.value = '50OFF';
code.trigger('input');
console.log(wrp.emitted('applied'));
//
// I NEVER see this on the outpout.
// How can I test it through a global event bus rather than
// an event emitted from the component instance?
//
EvtBus.$on('coupon-applied', () => {
console.log('coupon was applied through event bus');
});
// Passes, but not using EvtBus instance.
expect(wrp.emitted('applied')).toBeTruthy;
});
});
So, my doubt is how to test that the global event bus is emitting and listening to events inside components that use that event bus.
So, is it possible to test the global Event Bus using Vue Test Utils or I should use another approach?
If component is using global EventBus, eg that's imported outside of given component and assigned to window.EventBus, then it's possible to use global Vue instance to redirect $on or $emit events to wrapper's vm instance. That way you can proceed writing tests as if component is emitting via this.$emit instead of EventBus.$emit:
it('clicking "Settings" button emits "openSettings"', () => {
global.EventBus = new Vue();
global.EventBus.$on('openSettings', (data) => {
wrapper.vm.$emit('openSettings', data);
});
// component emits `EventBus.$emit('openSettings')`
expect(wrapper.emitted('openSettings')).toBeTruthy(); // pass
});
Well,
EvtBus.$on('coupon-applied', () => {
console.log('coupon was applied through event bus');
});
This code in your spec file won't be called because the mounted wrp component is not using the same EvtBus you are importing in your spec file above.
What you require to test this is an npm package named inject-loader so that you can provide your own implementation(stub) of the EvtBus dependency of your coupon code component.
Somewhat like this
const couponCodeInjector = require('!!vue-loader?inject!src/views/CouponCode');
const stubbedModules = {
'../EvtBus.js': {
$on : sandbox.spy((evtName, cb) => cb());
}
};
const couponCode = couponCodeInjector(stubbedModules);
and then in your unit test you can assert whether the stubbedModules['../EvtBus.js'].$on has been called or not when code.trigger('input');
PS: I haven't used vue-test-utils. So I don't know exactly how to the stubbing with this npm package.
But the main thing you need to do is to find a way to stub your EvtBus dependency in the CouponCode component in such a way that you can apply a spy on it and check whether that spy has been called or not.
Unit tests should focus on testing a single component in isolation. In this case, you want to test if the event is emitted, since that is the job of CouponCode.vue. Remember, unit tests should focus on testing the smallest units of code, and only test one thing at a time. In this case, we care that the event is emitted -- EventBus.test.js is where we test what happens when the event is emitted.
Noe that toBeTruthy is a function - you need (). expect(wrp.emitted('applied')).toBeTruthy is actually not passing, since you need () - at the moment, it is actually doing nothing -- no assertion is made.
What your assertion should look like is:
expect(wrp.emitted('applied')).toBeTruthy()
You can go one step further, and ensure it was only emitted once by doing something like expect(wrp.emitted().applied.length).toBe(1).
You then test InputBus in isolation, too. If you can post the code for that component, we can work through how to test it.
I worked on a big Vue app recently and contributed a lot to the main repo and documentation, so I'm happy to help out wherever I can.
Let me know if that helps or you need more guidance. If possible, post EventBus.vue as well.
I got the same issue with vue-test-utils and Jest. For me, createLocalVue() of vue-test-utils library fixed the issue. This function creates a local copy of Vue to use when mounting the component. Installing plugins on this copy of Vue prevents polluting the original Vue copy. (https://vue-test-utils.vuejs.org/api/options.html#localvue)
Adding this to your test file will fix the issue:
const EventBus = new Vue();
const GlobalPlugins = {
install(v) {
// Event bus
v.prototype.$bus = EventBus;
},
};
// create a local instance of the global bus
const localVue = createLocalVue();
localVue.use(GlobalPlugins);
jest.mock('#/main', () => ({
$emit: jest.fn(),
}));
Include this in code in your spec file at the very begining.
Note: '#/main' is the file from which you are importing Event Bus.

React Native: Jest mocking Platform

When writing unit tests for a React Native project I want to be able to test different snapshots based on different platforms.
I first tried jest.mock to mock Platform but seems to be async. This approach does work when I have two separate files, but I'd prefer to keep everything in one file if possible.
I tried jest.doMock because of this snippet from the documentation:
When using babel-jest, calls to mock will automatically be hoisted to the top of the code block. Use this method if you want to explicitly avoid this behavior.
https://facebook.github.io/jest/docs/en/jest-object.html#jestdomockmodulename-factory-options
However I'm still seeing undesirable results. When I console.log in the android test I see that Platform.OS is whatever I set the first doMock to be.
I also tried wrapping the mock in a beforeEach in a describe becasue I thought that might help with scoping
http://facebook.github.io/jest/docs/en/setup-teardown.html#scoping
describe('ios test', () => {
it('renders ui correctly', () => {
jest.doMock('Platform', () => {
const Platform = require.requireActual('Platform');
Platform.OS = 'ios';
return Platform;
});
const wrapper = shallow(<SomeComponent />);
const tree = renderer.create(wrapper).toJSON();
expect(tree).toMatchSnapshot();
});
});
describe('android test', () => {
it('renders ui correctly', () => {
jest.doMock('Platform', () => {
const Platform = require.requireActual('Platform');
Platform.OS = 'android';
return Platform;
});
const wrapper = shallow(<SomeComponent />);
const tree = renderer.create(wrapper).toJSON();
expect(tree).toMatchSnapshot();
});
});
Any ideas on how I can change the mock Platform for tests in the same file?
There are a lot of suggestions on how to solve this problem in another question, but none of them worked for me either, given the same requirements you have (tests for different OSs in the same suite file and in one test run).
I eventually worked around it with a somewhat clunky trivial helper function that can be mocked as expected in tests – something like:
export function getOS() {
return Platform.OS;
}
Use it instead of Platform.OS in your code, and then simply mock it in your tests, e.g.
it('does something on Android', () => {
helpers.getOS = jest.fn().mockImplementationOnce(() => 'android');
// ...
}
That did the trick; credit for the idea is due to this guy.

On console.log, ViewChild variable is undefined in unit test

I'm trying to test a component that has an #ViewChild annotation. One of the functions that I'm trying to test calls the #ViewChild's element for focus. However, when I try to log out the #ViewChild variable, it is always undefined. I thought componentFixture.detectChanges() would initiate the ElementRef, but it doesn't seem to.
Is there any way to make it so it isn't undefined?
You didn't show your code but, probably u have that undefined because you did your ViewChild like:
#ViewChild(MySubComponent)
instead of
#ViewChild('componentref')
and then in your template:
<my-sub-component #componentref></my-sub-component>
and of course you need to init your component with componentFixture.detectChanges()
I don't know which version of Angular2 you use and how you initialize your test suite but the detectChanges method on the ComponentFixture instance is responsible to set such fields.
Here is a sample test that shows this:
it('should set testElt', injectAsync([TestComponentBuilder], (tcb: TestComponentBuilder) => {
return tcb.createAsync(MyList).then((componentFixture: ComponentFixture) => {
expect(componentFixture.componentInstance.testElt).toBeUndefined();
componentFixture.detectChanges();
expect(componentFixture.componentInstance.testElt).toBeDefined();
var testElt = componentFixture.componentInstance.testElt;
expect(testElt.nativeElement.textContent).toEqual('Some test');
});
}));
See the corresponding plunkr: https://plnkr.co/edit/THMBXX?p=preview.

How to unit test API calls with mocked fetch() in react-native with Jest

In React Native I use fetch to perform network requests, however fetch is not an explicitly required module, so it is seemingly impossible to mock in Jest.
Even trying to call a method which uses fetch in a test will result in:
ReferenceError: fetch is not defined
Is there a way to test such API requests in react native with Jest?
Inside your test case you can mock any function you want by using Jest's mocks:
fetch = jest.fn(() => Promise.resolve());
This approach works only for the promise-based test cases (see pit in the Jest docs).
As far as fetch is an async function, you need to run all your tests using pit (read more about async tests here).
Another approach where you mock the global fetch object:
const mockSuccesfulResponse = (
status = 200,
method = RequestType.GET,
returnBody?: object
) => {
global.fetch = jest.fn().mockImplementationOnce(() => {
return new Promise((resolve, reject) => {
resolve({
ok: true,
status,
json: () => {
return returnBody ? returnBody : {};
},
});
});
});
};
The above helper method can be modified any way you want :-) Hope it helps someone
Rather than rolling your own mock, you can use the jest-fetch-mock npm package to override the global fetch object. That package allows you to set up fake responses and verify sent requests. See that link for extensive usage examples.
I solved this by adding isomorphic-fetch.
$ npm install --save isomorphic-fetch
and using it like
import fetch from 'isomorphic-fetch';
...
fetch('http://foo.com');
whatwg-fetch might work as well
Suppose you want to test resolve and reject cases, for this first you mock the fetch behaviour and then use Jest's rejects and resolves methods with with assertion block
function fetchTodos() {
return fetch(`${window.location.origin}/todos.json`)
.then(response => response.json())
.catch(error => console.log(error))
}
describe('fetchTodos', () => {
it('returns promise resolving to parsed response', () => {
global.fetch = jest.fn(() => Promise.resolve({ json: () => ''}))
expect(fetchTodos()).resolves.toBe('');
})
it('returns promise handling the error', async () => {
global.fetch = jest.fn(() => Promise.reject(''))
expect(fetchTodos()).rejects.toBe('')
})
})
As #ArthurDenture recommended, you can use fetch-mock, but there are some additional packages you will need to install to make it work with React Native and Jest:
$ npm install --save-dev fetch-mock
$ npm install --save-dev babel-plugin-transform-runtime
$ npm install --save-dev babel-preset-env
You can then mock fetch requests in your tests. Here is an example:
// __tests__/App.test.js
import React from 'react';
import App from '../App';
import fetchMock from 'fetch-mock';
import renderer from 'react-test-renderer';
it('renders without crashing', () => {
fetchMock.mock('*', 'Hello World!');
const rendered = renderer.create(<App />).toJSON();
expect(rendered).toBeTruthy();
});
Due to problems using fetch-mock with jest, I've release fetch-mock-jest. It basically gives the full fetch-mock api, but with a few jest-specific helpers, and works out of the box with jest, without needing to do any tricky wiring yourself
As shown in the react-testing-library documentation, you can use the jest.spyOn() function, which will mock the fetch function only for the next time it is called.
const fakeUserResponse = {token: 'fake_user_token'}
jest.spyOn(window, 'fetch').mockImplementationOnce(() => {
return Promise.resolve({
json: () => Promise.resolve(fakeUserResponse),
})
})
react-testing-library