Are there any libraries out there to mock localStorage?
I've been using Sinon.JS for most of my other javascript mocking and have found it is really great.
My initial testing shows that localStorage refuses to be assignable in firefox (sadface) so I'll probably need some sort of hack around this :/
My options as of now (as I see) are as follows:
Create wrapping functions that all my code uses and mock those
Create some sort of (might be complicated) state management (snapshot localStorage before test, in cleanup restore snapshot) for localStorage.
??????
What do you think of these approaches and do you think there are any other better ways to go about this? Either way I'll put the resulting "library" that I end up making on github for open source goodness.
Here is a simple way to mock it with Jasmine:
let localStore;
beforeEach(() => {
localStore = {};
spyOn(window.localStorage, 'getItem').and.callFake((key) =>
key in localStore ? localStore[key] : null
);
spyOn(window.localStorage, 'setItem').and.callFake(
(key, value) => (localStore[key] = value + '')
);
spyOn(window.localStorage, 'clear').and.callFake(() => (localStore = {}));
});
If you want to mock the local storage in all your tests, declare the beforeEach() function shown above in the global scope of your tests (the usual place is a specHelper.js script).
just mock the global localStorage / sessionStorage (they have the same API) for your needs.
For example:
// Storage Mock
function storageMock() {
let storage = {};
return {
setItem: function(key, value) {
storage[key] = value || '';
},
getItem: function(key) {
return key in storage ? storage[key] : null;
},
removeItem: function(key) {
delete storage[key];
},
get length() {
return Object.keys(storage).length;
},
key: function(i) {
const keys = Object.keys(storage);
return keys[i] || null;
}
};
}
And then what you actually do, is something like that:
// mock the localStorage
window.localStorage = storageMock();
// mock the sessionStorage
window.sessionStorage = storageMock();
The current solutions will not work in Firefox. This is because localStorage is defined by the html spec as being not modifiable. You can however get around this by accessing localStorage's prototype directly.
The cross browser solution is to mock the objects on Storage.prototype e.g.
instead of spyOn(localStorage, 'setItem') use
spyOn(Storage.prototype, 'setItem')
spyOn(Storage.prototype, 'getItem')
taken from bzbarsky and teogeos's replies here https://github.com/jasmine/jasmine/issues/299
Also consider the option to inject dependencies in an object's constructor function.
var SomeObject(storage) {
this.storge = storage || window.localStorage;
// ...
}
SomeObject.prototype.doSomeStorageRelatedStuff = function() {
var myValue = this.storage.getItem('myKey');
// ...
}
// In src
var myObj = new SomeObject();
// In test
var myObj = new SomeObject(mockStorage)
In line with mocking and unit testing, I like to avoid testing the storage implementation. For instance no point in checking if length of storage increased after you set an item, etc.
Since it is obviously unreliable to replace methods on the real localStorage object, use a "dumb" mockStorage and stub the individual methods as desired, such as:
var mockStorage = {
setItem: function() {},
removeItem: function() {},
key: function() {},
getItem: function() {},
removeItem: function() {},
length: 0
};
// Then in test that needs to know if and how setItem was called
sinon.stub(mockStorage, 'setItem');
var myObj = new SomeObject(mockStorage);
myObj.doSomeStorageRelatedStuff();
expect(mockStorage.setItem).toHaveBeenCalledWith('myKey');
This is what I do...
var mock = (function() {
var store = {};
return {
getItem: function(key) {
return store[key];
},
setItem: function(key, value) {
store[key] = value.toString();
},
clear: function() {
store = {};
}
};
})();
Object.defineProperty(window, 'localStorage', {
value: mock,
});
Are there any libraries out there to mock localStorage?
I just wrote one:
(function () {
var localStorage = {};
localStorage.setItem = function (key, val) {
this[key] = val + '';
}
localStorage.getItem = function (key) {
return this[key];
}
Object.defineProperty(localStorage, 'length', {
get: function () { return Object.keys(this).length - 2; }
});
// Your tests here
})();
My initial testing shows that localStorage refuses to be assignable in firefox
Only in global context. With a wrapper function as above, it works just fine.
Overwriting the localStorage property of the global window object as suggested in some of the answers won't work in most JS engines, because they declare the localStorage data property as not writable and not configurable.
However I found out that at least with PhantomJS's (version 1.9.8) WebKit version you could use the legacy API __defineGetter__ to control what happens if localStorage is accessed. Still it would be interesting if this works in other browsers as well.
var tmpStorage = window.localStorage;
// replace local storage
window.__defineGetter__('localStorage', function () {
throw new Error("localStorage not available");
// you could also return some other object here as a mock
});
// do your tests here
// restore old getter to actual local storage
window.__defineGetter__('localStorage',
function () { return tmpStorage });
The benefit of this approach is that you would not have to modify the code you're about to test.
You don't have to pass the storage object to each method that uses it. Instead, you can use a configuration parameter for any module that touches the storage adapter.
Your old module
// hard to test !
export const someFunction (x) {
window.localStorage.setItem('foo', x)
}
// hard to test !
export const anotherFunction () {
return window.localStorage.getItem('foo')
}
Your new module with config "wrapper" function
export default function (storage) {
return {
someFunction (x) {
storage.setItem('foo', x)
}
anotherFunction () {
storage.getItem('foo')
}
}
}
When you use the module in testing code
// import mock storage adapater
const MockStorage = require('./mock-storage')
// create a new mock storage instance
const mock = new MockStorage()
// pass mock storage instance as configuration argument to your module
const myModule = require('./my-module')(mock)
// reset before each test
beforeEach(function() {
mock.clear()
})
// your tests
it('should set foo', function() {
myModule.someFunction('bar')
assert.equal(mock.getItem('foo'), 'bar')
})
it('should get foo', function() {
mock.setItem('foo', 'bar')
assert.equal(myModule.anotherFunction(), 'bar')
})
The MockStorage class might look like this
export default class MockStorage {
constructor () {
this.storage = new Map()
}
setItem (key, value) {
this.storage.set(key, value)
}
getItem (key) {
return this.storage.get(key)
}
removeItem (key) {
this.storage.delete(key)
}
clear () {
this.constructor()
}
}
When using your module in production code, instead pass the real localStorage adapter
const myModule = require('./my-module')(window.localStorage)
Here is an exemple using sinon spy and mock:
// window.localStorage.setItem
var spy = sinon.spy(window.localStorage, "setItem");
// You can use this in your assertions
spy.calledWith(aKey, aValue)
// Reset localStorage.setItem method
spy.reset();
// window.localStorage.getItem
var stub = sinon.stub(window.localStorage, "getItem");
stub.returns(aValue);
// You can use this in your assertions
stub.calledWith(aKey)
// Reset localStorage.getItem method
stub.reset();
credits to
https://medium.com/#armno/til-mocking-localstorage-and-sessionstorage-in-angular-unit-tests-a765abdc9d87
Make a fake localstorage, and spy on localstorage, when it is caleld
beforeAll( () => {
let store = {};
const mockLocalStorage = {
getItem: (key: string): string => {
return key in store ? store[key] : null;
},
setItem: (key: string, value: string) => {
store[key] = `${value}`;
},
removeItem: (key: string) => {
delete store[key];
},
clear: () => {
store = {};
}
};
spyOn(localStorage, 'getItem')
.and.callFake(mockLocalStorage.getItem);
spyOn(localStorage, 'setItem')
.and.callFake(mockLocalStorage.setItem);
spyOn(localStorage, 'removeItem')
.and.callFake(mockLocalStorage.removeItem);
spyOn(localStorage, 'clear')
.and.callFake(mockLocalStorage.clear);
})
And here we use it
it('providing search value should return matched item', () => {
localStorage.setItem('defaultLanguage', 'en-US');
expect(...
});
I found that I did not need to mock it. I could change the actual local storage to the state I wanted it via setItem, then just query the values to see if it changed via getItem. It's not quite as powerful as mocking as you can't see how many times something was changed, but it worked for my purposes.
I decided to reiterate my comment to Pumbaa80's answer as separate answer so that it'll be easier to reuse it as a library.
I took Pumbaa80's code, refined it a bit, added tests and published it as an npm module here:
https://www.npmjs.com/package/mock-local-storage.
Here is a source code:
https://github.com/letsrock-today/mock-local-storage/blob/master/src/mock-localstorage.js
Some tests:
https://github.com/letsrock-today/mock-local-storage/blob/master/test/mock-localstorage.js
Module creates mock localStorage and sessionStorage on the global object (window or global, which of them is defined).
In my other project's tests I required it with mocha as this: mocha -r mock-local-storage to make global definitions available for all code under test.
Basically, code looks like follows:
(function (glob) {
function createStorage() {
let s = {},
noopCallback = () => {},
_itemInsertionCallback = noopCallback;
Object.defineProperty(s, 'setItem', {
get: () => {
return (k, v) => {
k = k + '';
_itemInsertionCallback(s.length);
s[k] = v + '';
};
}
});
Object.defineProperty(s, 'getItem', {
// ...
});
Object.defineProperty(s, 'removeItem', {
// ...
});
Object.defineProperty(s, 'clear', {
// ...
});
Object.defineProperty(s, 'length', {
get: () => {
return Object.keys(s).length;
}
});
Object.defineProperty(s, "key", {
// ...
});
Object.defineProperty(s, 'itemInsertionCallback', {
get: () => {
return _itemInsertionCallback;
},
set: v => {
if (!v || typeof v != 'function') {
v = noopCallback;
}
_itemInsertionCallback = v;
}
});
return s;
}
glob.localStorage = createStorage();
glob.sessionStorage = createStorage();
}(typeof window !== 'undefined' ? window : global));
Note that all methods added via Object.defineProperty so that them won't be iterated, accessed or removed as regular items and won't count in length. Also I added a way to register callback which is called when an item is about to be put into object. This callback may be used to emulate quota exceeded error in tests.
Unfortunately, the only way we can mock the localStorage object in a test scenario is to change the code we're testing. You have to wrap your code in an anonymous function (which you should be doing anyway) and use "dependency injection" to pass in a reference to the window object. Something like:
(function (window) {
// Your code
}(window.mockWindow || window));
Then, inside of your test, you can specify:
window.mockWindow = { localStorage: { ... } };
This is how I like to do it. Keeps it simple.
let localStoreMock: any = {};
beforeEach(() => {
angular.mock.module('yourApp');
angular.mock.module(function ($provide: any) {
$provide.service('localStorageService', function () {
this.get = (key: any) => localStoreMock[key];
this.set = (key: any, value: any) => localStoreMock[key] = value;
});
});
});
Need to interact with stored data
A quite short approach
const store = {};
Object.defineProperty(window, 'localStorage', {
value: {
getItem:(key) => store[key]},
setItem:(key, value) => {
store[key] = value.toString();
},
clear: () => {
store = {};
}
},
});
Spy with Jasmine
If you just need these functions to spy on them using jasmine it will be even shorter and easier to read.
Object.defineProperty(window, 'localStorage', {
value: {
getItem:(key) => {},
setItem:(key, value) => {},
clear: () => {},
...
},
});
const spy = spyOn(localStorage, 'getItem')
Now you don't need a store at all.
For those wanting to mock localstorage and not simply spy on it, this worked for me:
Storage.prototype.getItem = jest.fn(() => 'bla');
Source:
https://github.com/facebook/jest/issues/6858
I know OP specifically asked about mocking, but arguably it's better to spy rather than mock. And what if you use Object.keys(localStorage) to iterate over all available keys? You can test it like this:
const someFunction = () => {
const localStorageKeys = Object.keys(localStorage)
console.log('localStorageKeys', localStorageKeys)
localStorage.removeItem('whatever')
}
and the test code will be like follows:
describe('someFunction', () => {
it('should remove some item from the local storage', () => {
const _localStorage = {
foo: 'bar', fizz: 'buzz'
}
Object.setPrototypeOf(_localStorage, {
removeItem: jest.fn()
})
jest.spyOn(global, 'localStorage', 'get').mockReturnValue(_localStorage)
someFunction()
expect(global.localStorage.removeItem).toHaveBeenCalledTimes(1)
expect(global.localStorage.removeItem).toHaveBeenCalledWith('whatever')
})
})
No need for mocks or constructors. Relatively few lines, too.
None of these answers are completely accurate or safe to use. Neither is this one but it is as accurate as I wanted without figuring out how to manipulate getters and setters.
TypeScript
const mockStorage = () => {
for (const storage of [window.localStorage, window.sessionStorage]) {
let store = {};
spyOn(storage, 'getItem').and.callFake((key) =>
key in store ? store[key] : null
);
spyOn(storage, 'setItem').and.callFake(
(key, value) => (store[key] = value + '')
);
spyOn(storage, 'removeItem').and.callFake((key: string) => {
delete store[key];
});
spyOn(storage, 'clear').and.callFake(() => (store = {}));
spyOn(storage, 'key').and.callFake((i: number) => {
throw new Error(`Method 'key' not implemented`);
});
// Storage.length is not supported
// Property accessors are not supported
}
};
Usage
describe('Local storage', () => {
beforeEach(() => {
mockStorage();
});
it('should cache a unit in session', () => {
LocalStorageService.cacheUnit(testUnit);
expect(window.sessionStorage.setItem).toHaveBeenCalledTimes(1);
expect(window.sessionStorage.getItem(StorageKeys.units)).toContain(
testUnit.id
);
});
});
Caveats
With localStorage you can do window.localStorage['color'] = 'red';
this will bypass the mock.
window.localStorage.length will bypass this mock.
window.localStorage.key throws in this mock as code relying on this can not be tested by this mock.
Mock correctly separates local and session storage.
Please also see: MDN: Web Storage API
Related
How can I pass a variable between plugins in Rollup?
What I've tried:
// plugin-a.js
const pluginA = () => {
return {
name: 'pluginA',
async options(options) {
options.define = options.define || {};
options.define['foo'] = 'bar';
}
}
}
// plugin-b.js
const pluginB = (options = {}) => {
return {
name: 'pluginB',
buildStart: async (options) => {
console.log(options)
}
}
}
I'm getting a warning:
(!) You have passed an unrecognized option
Unknown input options: define. Allowed options: acorn, acornInjectPlugins, cache, context, experimentalCacheExpiry, external, inlineDynamicImports, input, makeAbsoluteExternalsRelative, manualChunks, maxParallelFileOps, maxParallelFileReads, moduleContext, onwarn, perf, plugins, preserveEntrySignatures, preserveModules, preserveSymlinks, shimMissingExports, strictDeprecations, treeshake, watch
It seems passing data should be done by what Rollup refers to as Direct plugin communication. This is working for me. I feel this is very hard coupled though.
function parentPlugin() {
return {
name: 'parent',
api: {
//...methods and properties exposed for other plugins
doSomething(...args) {
// do something interesting
}
}
// ...plugin hooks
};
}
function dependentPlugin() {
let parentApi;
return {
name: 'dependent',
buildStart({ plugins }) {
const parentName = 'parent';
const parentPlugin = plugins.find(plugin => plugin.name === parentName);
if (!parentPlugin) {
// or handle this silently if it is optional
throw new Error(`This plugin depends on the "${parentName}" plugin.`);
}
// now you can access the API methods in subsequent hooks
parentApi = parentPlugin.api;
},
transform(code, id) {
if (thereIsAReasonToDoSomething(id)) {
parentApi.doSomething(id);
}
}
};
}
There's also Custom module meta-data, however when I read the meta I always get null.
Im trying to write a Jest test case where code involved localstorage access.
While running test case is failing saying cant read property.
What is the way we need to write jest test case where localstorage.getItem() is involved
function myLocal(){
var value= localStorage.getItem('slot').time
return value
}
while running above sample code, Jest is throwing below error
TypeError: Cannot read property 'time' of null
Make your function testable:
function getTime(storage) {
var value = storage.getItem('slot').time
return value
}
Then use it in your application like that:
getTime(localStorage);
And test it like that:
const mockGetItem = jest.fn();
mockGetItem.mockReturnValue({time: '16:00'});
expect(getTime({getItem: mockGetItem})).toBe('16:00');
expect(mockGetItem).toHaveBeenCalledWith('slot');
You can mock it like anything else. This example is taken from some older version of jest-preset-angular i think:
const mock = () => {
let storage: { [key: string]: string } = {};
return {
getItem: (key: string) => (key in storage ? storage[key] : null),
setItem: (key: string, value: string) => (storage[key] = value || ''),
removeItem: (key: string) => delete storage[key],
clear: () => (storage = {})
};
};
Object.defineProperty(window, 'localStorage', { value: mock() });
Object.defineProperty(window, 'sessionStorage', { value: mock() });
No changes in your code. Of course you have to set the items you want to get first.
UPDATE:
I just noticed you are using plain JavaScript, not TypeScript. In that case you have to modify the mock:
const mock = function() {
const storage = {};
return {
getItem: (key) => (key in storage ? storage[key] : null),
setItem: (key, value) => (storage[key] = value || ''),
removeItem: (key) => delete storage[key],
clear: () => (storage = {})
};
};
Also, the example you posted in comments does not have a window object available, so you might have to mock that as well:
const window = {
localStorage: mock();
};
// or if you only use localStorage without window, this might suffice:
localStorage = mock();
Since the latest release of JSDom, I'm not able to mock localStorage anymore.
I've tried the following methods:
Object.defineProperty(window, 'localStorage', {value: LocalStorageMock})
window.localStorage = LocalStorageMock;
jest.spyOn(window.localStorage, 'setItem')
Any of those methods not worked for me, I get always the original localStorage.
setItemSpy = jest.spyOn(Storage.prototype, 'setItem'); works for me.
Saw this fix here: https://github.com/facebook/jest/issues/6858#issuecomment-413677180
I actually ran into this same issue when updating Jest, not sure if that's what happened to you but I found this fix here:
https://github.com/facebook/jest/issues/6766
From OlivierB-OB:
As a temporary workaround you can install jsdom "11.11.0" (exact) as a dev-dependency in your package. jest-environment-jsdom should then use this version instead of the lastest "11.12.0" causing the behavior.
Cheers!
After that I mocked localstorage in test setup and spying was back to normal.
And an implementation of localstorage mock: https://github.com/facebook/jest/issues/2098
lacks removeItem though, so you might need to add it.
You can use the dom-storage package available via npm:
const Storage = require('dom-storage');
global.localStorage = new Storage(null, { strict: true });
global.sessionStorage = new Storage(null, { strict: true });
We use the latest release of jsdom for our unit tests and the above method has worked great.
I've create a function that mocks localStorage. It implements only two methods getItem and setItem. You can easily add other methods if needed.
export const localStorageImpl = {
register: () => {
let storage = (window as any).customLocalStorage;
if(storage) {
return {
storage,
methods: (window as any).customLocalStorageMethods
}
}
storage = (window as any).customLocalStorage = {} as any;
const setItem = jest.spyOn(Storage.prototype, 'setItem');
setItem.mockImplementation((key, value) => {
storage[key] = value;
});
const getItem = jest.spyOn(Storage.prototype, 'getItem');
getItem.mockImplementation((key) => {
return storage[key];
});
const methods = (window as any).customLocalStorageMethods = {
setItem,
getItem
};
return {
storage,
methods
}
},
unregister: () => {
const methods = (window as any).customLocalStorageMethods;
if(methods){
const { setItem, getItem } = methods as { setItem: jest.SpyInstance<void, [key: string, value: string]>, getItem: jest.SpyInstance<string, [key: string]> };
setItem.mockReset();
getItem.mockReset();
}
delete (window as any).customLocalStorageMethods;
delete (window as any).customLocalStorage;
}
}
Usage:
it('should mock localStorage', () => {
const { methods } = localStorageImpl.register(); // mock localStorage
const { getByTestId } = render(<Root />);
fireEvent.click(getByTestId('column-size'));
expect(methods.setItem).toBeCalledTimes(1);
localStorageImpl.unregister();
});
I'm a very beginner with testing and started using jest. This function I have saves data in chrome.storage.local and I want to test if chrome.storage.local called 3 times. Here is the function:
saveData: function(){
chrome.storage.local.set({'blackList': bgModule.blackList}, function() {});
chrome.storage.local.set({'pastDays': bgModule.pastDays}, function() {});
chrome.storage.local.set({'websiteList': bgModule.websiteList}, function() {});
}
and here is my test:
const bgModule = require("../../app/Background/background.js");
const chrome = {
storage: {
local: {
set: function() {},
get: function() {}
}
}
};
let blackListStub = bgModule.blackList;
let pastDaysStub = [
{day: "day1"},
{day2: "day2"},
{day3: "day3"}];
let websiteListStub = [
{websiteName: "facebook.com"},
{websiteName: "stackoverflow.com"},
{websiteName: "github.com"}];
it ("should save data in local storage", () => {
spyOn(bgModule, 'saveData');
bgModule.saveData();
const spy = spyOn(chrome.storage.local, 'set');
spy({'blackList' : blackListStub});
spy({'pastDays' : pastDaysStub});
spy({'websiteList' : websiteListStub});
expect(spy).toHaveBeenCalledWith({'blackList' : blackListStub});
expect(spy).toHaveBeenCalledWith({'pastDays' : pastDaysStub});
expect(spy).toHaveBeenCalledWith({'websiteList' : websiteListStub});
expect(bgModule.saveData).toHaveBeenCalledTimes(1);
expect(spy).toHaveBeenCalledTimes(3);
});
Test passes but it's incorrect. I want to make it work so when I change saveData it will break the test. The test I have has everything hardcoded into it and doesn't depend on saveData at all. I looked for example and tutorial materials and couldn't find anything for this case. Any help or direction I should take would be very helpful.
After help and correct answer with use of global.chrome refactored test looks like this:
it ("should save data in local storage", () => {
bgModule.saveData();
expect(chrome.storage.local.set).toHaveBeenCalledTimes(3);
});
The easiest thing would be to use dependency injection, so instead of calling chrome.storage.local directly, passed it as an argument to your function that then can be easily replaced by a mock in your test.
The other way would be to add it as a global variable into your test environment like this:
const get = jest.fn()
const set = jest.fn()
global.chrome = {
storage: {
local: {
set,
get
}
}
I'd like to augment, but not completely replace, instances of a mocked constructor in a Jest unit test.
I want to add a few values to the instance, but keep the auto-mocked goodness of Jest.
For example:
A.js
module.exports = class A {
constructor(value) {
this.value = value;
}
getValue() {
return this.value;
}
}
To get some auto-mock awesomeness:
jest.mock('./A');
With the automock, instances have a mocked .getValue() method, but they do not have the .value property.
A documented way of mocking constructors is:
// SomeClass.js
module.exports = class SomeClass {
m(a, b) {}
}
// OtherModule.test.js
jest.mock('./SomeClass'); // this happens automatically with automocking
const SomeClass = require('./SomeClass')
const mMock = jest.fn()
SomeClass.mockImplementation(() => {
return {
m: mMock
}
})
const some = new SomeClass()
some.m('a', 'b')
console.log('Calls to m: ', mMock.mock.calls)
Using that approach for A:
jest.mock('./A');
const A = require('./A');
A.mockImplementation((value) => {
return { value };
});
it('does stuff', () => {
const a = new A();
console.log(a); // -> A { value: 'value; }
});
The nice thing about that is you can do whatever you want to the returned value, like initialize .value.
The downsides are:
You don't get any automocking for free, e.g. I'd need to add .getValue() myself to the instance
You need to have a different jest.fn() mock function for each instance created, e.g. if I create two instances of A, each instance needs its own jest.fn() mock functions for the .getValue() method
SomeClass.mock.instances is not populated with the returned value (GitHub ticket)
One thing that didn't work (I was hoping that maybe Jest did some magic):
A.mockImplementation((value) => {
const rv = Object.create(A.prototype); // <- these are mocked methods
rv.value = value;
return rv;
});
Unfortunately, all instances share the same methods (as one would expect, but it was worth a shot).
My next step is to generate the mock, myself, via inspecting the prototype (I guess), but I wanted to see if there is an established approach.
Thanks in advance.
Turns out this is fixed (as of jest 24.1.0) and the code in the question works, as expected.
To recap, given class A:
A.js
module.exports = class A {
constructor(value) {
this.value = value;
}
setValue(value) {
this.value = value;
}
}
This test will now pass:
A.test.js
jest.mock('./A');
const A = require('./A');
A.mockImplementation((value) => {
const rv = Object.create(A.prototype); // <- these are mocked methods
rv.value = value;
return rv;
});
it('does stuff', () => {
const a = new A('some-value');
expect(A.mock.instances.length).toBe(1);
expect(a instanceof A).toBe(true);
expect(a).toEqual({ value: 'some-value' });
a.setValue('another-value');
expect(a.setValue.mock.calls.length).toBe(1);
expect(a.setValue.mock.calls[0]).toEqual(['another-value']);
});
The following worked for me:
A.mockImplementation(value => {
const rv = {value: value};
Object.setPrototypeOf(rv, A.prototype);
return rv
})