setting localStorage in beforeEach() fails occasionally

I have a system with JWT authentication and, as I understand is a best practice, set the localStorage in a beforeEach() to ensure the user is logged in before each test.

describe('A test', function() {
    beforeEach(function() {
        if (this.currentUser) {
            localStorage.setItem('currentUser', this.currentUser);
            localStorage.setItem('token', this.token);
        }
    });
   it('does a test', function() {});
   it('does another test', function() {});

Occasionally, one of the tests fails as it perceives the user is not logged in. This seems random, i.e. the first one can pass and the second then fail. (Like, once in 500 it() tests).

As it is not reproducible it is rather hard to debug, as it only happens about once in 30 minutes running headless on a CI server. I would say however that it seems to have gotten worse with 3.3.1. Earlier, it was so rare that I could live with it.

I am using Electron browser.

[danatemple]

Thanks - I look forward to #686 being implemented. This is exactly what is needed.

For info, the workaround https://github.com/cypress-io/cypress/issues/461#issuecomment-392070888 (or my similar one, on the comment right below that one!) is what is not working 100%.

As I don’t use localStorage for anything that I don’t want to persist, the following does the trick reliably:

Cypress.LocalStorage.clear = function (keys, ls, rs) {
   return;
}

[danatemple]

Having done more testing now, I can confirm that the tests are absolutely rock solid if I prevent the LocalStorage.clear from having an effect, whereas the unreliability exists if I use the official workaround of trying to restore localStorage in a beforeEach before each test.

It seems there really needs to be a reliable way to keep DOM-critical local storage from getting deleted at all, even temporarily? I know the philosophy of cleaning up each time, but for an SPA with JWT, the user login is integral to the app state. The DOM state is after all allowed to persist.

Otherwise, each it() will need to re-start the app 100% from scratch with a full page load and reset the entire DOM, which for an SPA especially removes the point of having the it() level of test hierarchy.