Cypress Parallel Test Execution: Missing Automatic localStorage/sessionStorage Reset Between Workers

Direct answers

1. Configuration flag? No — and none is needed. Cypress Cloud parallel workers each spin up a fresh browser profile on a separate machine/container, so localStorage/sessionStorage written by one worker can never leak into another. Cross‑worker contamination is structurally impossible.
2. Recommended pattern for zero‑duplication isolation? You already have it. Since Cypress 12, testIsolation: true (the default) resets the entire browser context — storage, cookies, page — before every spec file and before every test. If you still want a single global hook for custom cleanup, put it in cypress/support/e2e.js:

   // cypress/support/e2e.js
   beforeEach(() => {
     // runs once per test across every spec
     // cy.clearLocalStorage() is redundant but harmless here
   });
   

3. Roadmap item? Not applicable — the behavior you’re asking for has been the default since Cypress 12 (2022).

Why the premise differs from reality

The question assumes storage persists across parallel workers. In Dashboard‑orchestrated parallelism (cypress run --parallel --record), each worker gets its own isolated browser profile. Within a single worker, testIsolation clears storage between specs and between tests. The only way to see leakage is:

• Running a third‑party “parallel” tool that re‑uses one browser profile (not Cypress Cloud).
• Explicitly setting testIsolation: false in cypress.config.js.

Verify in your project (30 seconds)

1. Confirm testIsolation is not overridden:

   // cypress.config.js
   export default defineConfig({
     e2e: { testIsolation: true } // default, can be omitted
   });
   

2. Create two specs:

   // cypress/e2e/spec-a.cy.js
   it('writes sentinel', () => {
     localStorage.setItem('worker-token', 'spec-a');
   });
   
   // cypress/e2e/spec-b.cy.js
   it('asserts isolation', () => {
     expect(localStorage.getItem('worker-token')).to.be.null;
   });
   

3. Run npx cypress run --parallel --record (requires Dashboard project). Spec B will pass — the key is absent.

When you do need shared state

Use cy.session() for authenticated sessions or expensive setup. It coexists with test isolation and is the supported way to cache state across tests within a spec.

One diagnostic that would change the advice

Are you using Cypress Cloud (--parallel --record) or a local parallel runner (e.g., cypress-parallel, xargs, custom script) that launches multiple browsers on the same machine? If the latter, you do need explicit cleanup in the support file because the browser profile is shared.