Canonical, dated answers for coding agents — every entry states when it was true and which versions it applies to, so your context never goes stale.
Vitest 5.0.0 shipped 2026-09-03 (current 5.0.3). It needs Node ^22.12 and Vite >= 6.4. Mocks are cleared before each test by default, test.sequential was removed, unawaited async assertions fail, vi.mock must be top-level, and deprecated entry points were removed.
Cypress 16.0.0 shipped 2026-09-01 (current 16.1.1, 2026-09-29). It removes Cypress.env() (use cy.env()/Cypress.expose()), cy.exec() and cy.end(), intercepts Chrome/Edge traffic natively, requires Node 22/24/26+, and raises component-testing minimums (Vite 8, Angular 21, Next 15.0.4).
Agents optimistically claim success. Counter with: reproduce first, fix, prove the fix on the ORIGINAL repro, run the project gates, and report honestly what was and was not verified.
Jest 30.0.0 shipped 2025-06-10; current is 30.5.2 (2026-09-18). It removes the toBeCalled*/toThrowError aliases, renames testPathPattern to testPathPatterns, drops Node 14/16/19/21/23, requires TS 5.4+ and bundles jsdom 26.
Fast unit base, integration against real DB containers, thin E2E on critical paths. New since agents: verification tests (does the reproduction actually pass) and eval suites for AI features count as tests in CI.
Playwright (1.5x→1.6x line through 2026) ships monthly; aria-snapshot locators, improved UI mode and trace viewer make it the default E2E choice. Chromium/Firefox/WebKit stay in lockstep.
Small golden-task suites per product area, run on every prompt/model/context change; LLM-as-judge for open-ended tasks with spot-checked human calibration. Vendor benchmarks are marketing; your evals are the product.
pytest 9.0 (2026) removes years of deprecated APIs, tightens assertion rewriting and collection, and targets modern Python versions. Most suites upgrade cleanly in minutes.
JUnit 6 (2026) aligns the platform APIs, requires Java 17+, and ships a rebuilt documentation site. For new JVM projects it is the unambiguous default over JUnit 4/5 legacy modes.
Vitest 4.0 (Oct 2025) marks Browser Mode stable, adds visual regression testing and Playwright trace viewer. Snapshot format changed — regenerate on upgrade.
Storybook 9 (Jun 2025) cuts bundle size nearly in half, reorganizes around tags, ships story globals and unifies component testing (Vitest + Playwright) inside Storybook.