mock-local-storage

Mock lodcalStorage for headless unit tests

Inspired by StackOverflow answers and wrapped into rpm package to be used with mocha.

Motivation

I need to mock out localStorage to run tests of cache implementation with mocha in console (without browser).

Installation

npm install mock-local-storage --save-dev

Usage

mocha -r mock-local-storage

Mocha will require module, which will replace localStorage and sessionStorage on the global object.

There are some caveats with using index operator, though. Browser's localStorage works with strings and stringifyes objects stored via localStorage[key] notation, but this implementation does not.

Additionally, test code can provide 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();
        // remove callback
        localStorage.itemInsertionCallback = null;
    });
    it('emulate quota exceeded error', () => {
        localStorage.length.should.equal(0);
        // register callback
        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) {
                // handle quota exceeded error
                handled = true;
            }
        }
        handled.should.be.true;
        localStorage.length.should.equal(5);
    });
});

Tests

npm install
npm test

License

MIT