Mistake 4/14: Same data breaks Playwright group tests

Running tests together? Same " test@test.com " makes workers fight over one user. Quiet fails everywhere. I reviewed a test suite last week where hardcoded data completely killed their pipeline stability. Worker 1 passes, Workers 2-5 throw "email already exists." BEFORE : Tests fight each other test ( ' register new user ' , async ({ page }) => { await page . getByLabel ( ' Email ' ). fill ( ' test@test.com ' ); // Worker 1: passes. Workers 2-5: fail instantly }); AFTER : The Factory + JSON Combo Keep your hacks and limits in a static JSON file. Use a Faker factory for everything else. Zero collisions! import { faker } from ' @faker-js/faker ' ; import invalidInputs from ' ./invalid-inputs.json ' ; // 1. Factory function for dynamic, unique runs export function createTestUser () { return { email : `test- ${ Date . now ()} - ${ faker . string . alphanumeric ( 5 )} @test.com` , password : faker . internet . password ({ length : 12 }) }; } test ( ' happy path: zero collisions ' , async ({