mock-local-storage
Mock localStorage
for headless unit tests
Inspired by StackOverflow answers and wrapped into npm package.
Moving Notice
This package has moved from the letsrock-today repository into
KaiSforza's GitLab repository.
There is a copy of the code in Github, as well, but issues and pull
requests will only be watched in Gitlab.
Motivation
Used to mock localStorage
to run headless tests of cache implementation in terminal (ie. without browser).
Installation
npm install mock-local-storage --save-dev
Usage
Mocha
Require in Mocha, which will replace localStorage
and sessionStorage
on the global
and window
objects:
mocha --require mock-local-storage
If you are using jsdom-global
, make sure it is required before mock-local-storage
:
mocha --require jsdom-global --require mock-local-storage
Other testing frameworks
In a node environment you can mock the window.localStorage
as follows:
global.window = {}
import 'mock-local-storage'
window.localStorage = global.localStorage
This is very useful when you want to run headless tests on code meant for the browser that use localStorage
You can even store this in a file that is reused across tests:
mock-localstorage.js
global.window = {}
import 'mock-local-storage'
window.localStorage = global.localStorage
using-localstorage.test.js
import './mock-localstorage'
Besides mocking of conventional localStorage
interface, this implementation provides
a way for test code to register a callback to be invoked on item insertion.
Mock implementation will invoke it when localStorage.setItem()
is called
(but not with localStorage[key]
notation).
It can be used to emulate allocation errors, like this:
describe('test with mock localStorage', () => {
afterEach(() => {
localStorage.clear();
localStorage.itemInsertionCallback = null;
});
it('emulate quota exceeded error', () => {
localStorage.length.should.equal(0);
localStorage.itemInsertionCallback = (len) => {
if (len >= 5) {
let err = new Error('Mock localStorage quota exceeded');
err.code = 22;
throw err;
}
};
let handled = false;
try {
for (let i = 0; i < 10; ++i) {
localStorage.setItem(i, i);
}
} catch (e) {
if (e.code == 22) {
handled = true;
}
}
handled.should.be.true;
localStorage.length.should.equal(5);
});
});
Caveats
There are some caveats with using index
operator. Browser's localStorage
works with strings and stringifyes objects stored via localStorage[key]
notation,
but this implementation does not.
localStorage.itemInsertionCallback
won't be invoked with localStorage[key]
notation.
Tests
npm install
npm test
Bugs, issues, MRs, participation, contribution
Please feel free to send us occusionall MRs along with unit tests,
we'll merge them if they successfully build and pass unit tests.
Consider to always provide unit tests, illustrating your problem, along with PR to avoid future regression.
License
MIT