Testing

Core Rules

• Assert public behavior through editor APIs, plugin APIs, hooks, transforms, or rendered output. Do not assert private state, call order, or implementation detail when public behavior already proves the contract.
• Prefer file-ranked batches over package sweeps. Package sweeps are for early broad passes, not the endgame.
• Do not use coverage to justify testing files with no meaningful contract.
• Bun globals come from tooling/config/global.d.ts. Do not import describe, it, expect, mock, spyOn, or other globals from bun:test.
• Use *.spec.ts[x] for the fast lane and *.slow.ts[x] for the slow lane.
• Keep helpers package-local. Never import a helper from another spec file.
• No spec should import another spec.
• Put compile-only type contracts in type-tests/, not mixed into runtime specs.
• Titles should describe behavior semantically, not echo raw option names.
• Prefer explicit assertions over snapshots by default.
• Delete skipped tests, commented-out tests, and dead placeholder cases. Do not preserve wishful thinking.
• No fake smoke tests.
• No app-registry imports in package tests.
• Do not add package devDependencies just to support cross-package or app-shaped test setups. If a test needs other package kits, app aliases, or multi-package wiring, move it to apps/www/src/__tests__/package-integration.
• When adding tests, inspect fast-suite outliers with bun run test:profile. bun run test:slowest is the hard gate. If a fast-suite spec crosses the thresholds in tooling/config/test-suites.mjs, rename it to *.slow.ts[x].
• Do not trust a fast laptop. Treat the local warning zone as real debt before CI proves you wrong: 60ms/test or 120ms/file is already a move candidate, especially for React-heavy specs.
• For borderline cases, run pnpm test:slowest -- --top 25 --rerun-each 3 and move repeat offenders before they drift over the CI line.
• Treat known third-party resource logs and serializer fallback warnings as test noise. Suppress them narrowly in the shared Bun setup at tooling/config/bunTestSetup.ts, not by changing runtime code or sprinkling per-spec console mocks.

Seam Selection

• Use createEditor from @platejs/slate for pure Slate query, transform, interface, and history contracts.
• Use createSlateEditor for non-React plugin or editor wiring:
  • plugin option stores
  • selector extension
  • pure plugin API composition
  • pure transform composition
  • parser and deserializer contracts
  • HTML insertData
  • DnD-style contracts
• Use createPlateEditor only when the contract is genuinely Plate-specific.
• Use rendered React tests only when the contract is genuinely React-specific: hooks, providers, stores, DOM behavior, or rerender semantics.
• Remaining createPlateEditor usage is a reviewed allowlist, not a future cleanup queue.

File Organization

• File-scoped specs live beside the implementation.
• Keep __tests__/ only for:
  • package-local helpers
  • fixture banks
  • intentionally split multi-file behavior suites
  • intentionally kept integration suites
• Move lone file-scoped specs out of __tests__/.
• Collapse tiny split suites into one adjacent table-driven file when the only variation is fixture shape.
• Action helpers may create the editor and perform the transform, but assertions stay in the it() body.
• Rule-action helpers should return the editor and other setup results, not assert internally.
• For composition-heavy suites, extract focused helpers before adding more inline setup. Small helpers like getSortedKeys(...) and createStoreEditor(...) beat repeated editor construction sludge.

Fixtures And Assertions

• Use JSX hyperscript only when tree shape or selection shape is the contract.
• Use plain object fixtures for option, state, and pure helper tests.
• Use a real editor object only when editor-root semantics matter. NodeApi and ElementApi do not treat plain { children: [...] } objects the same way as real editors.
• Keep inputs and outputs small.
• Use it.each for small behavior matrices.
• In this Bun + Testing Library setup, prefer render-returned queries over screen.
• Snapshots are allowed only when serialized text, AST, or similar output is the contract and inline assertions would be worse.
• Whitespace-sensitive serializer outputs should prefer direct toBe(...) string assertions.
• Avoid toHaveStyle here. Use direct style-property assertions instead.
• After broad title renames on snapshot-backed suites, delete and regenerate the snapshot file. bun test -u updates and adds keys, but does not reliably prune dead ones.

Cleanup Heuristics

• Score files before cleanup waves instead of skimming randomly.
• Use fresh lcov after each pass. Do not keep working from a stale hotspot map.
• Rewrite large hotspot specs before chasing broad title debt. Bigger signal first.
• Scan title debt across:
  • plain string titles
  • it.each(...) format strings
  • String.raw titles
  • snapshot keys derived from those titles
• Scan for commented-out it, test, and describe blocks during dead-spec cleanup waves.
• End cleanup waves with repo scans for:
  • skipped tests
  • commented-out tests
  • cross-spec imports
  • placeholder titles
  • non-allowlisted createPlateEditor seams
• Use bun run test:profile for the fast suite when deciding whether a spec belongs in the slow lane. pnpm test:slowest and pnpm check enforce those thresholds.
• For rule-override hotspots, extract one editor helper and table-drive repeated node-type cases instead of cloning the same transform assertions.
• For plugin-composition hotspots, extract helpers before adding more inline setup.
• Adapt upstream invariants when local runtime semantics differ. Keep the invariant, rewrite the fixture around the real public contract.
• Treat tiny one-branch crumbs as crumbs. Do not let a coverage number talk you into fake work.
• Penalize giant files with poor test ROI unless they hold a central contract you actually care about during the next rewrite.

Package Rules

autoformat

• Use package-local rule arrays.
• Use KEYS or base plugins, not React plugin .key.
• Add only the base plugins a rule actually needs.
• Collapse tiny mark or block suites into matrices when the contract is the same.
• Do not import AutoformatKit or app registries in package tests.
• If an autoformat case needs cross-package behavior like code-block wiring or app-owned integration setup, move it to apps/www/src/__tests__/package-integration instead of expanding packages/autoformat/package.json.

markdown

• Configure MarkdownPlugin locally in the package helper.
• Do not import MarkdownKit or any app registry from apps/www.
• Prefer direct string assertions for tiny whitespace-sensitive serializer outputs.

ai / streaming markdown

• Keep one mixed-document smoke case.
• Add a few explicit chunk-boundary tests.
• Do not hide streaming behavior behind snapshots or giant hand-written trees.

core

• Use createSlateEditor for:
  • pure plugin option stores
  • selector extension
  • plugin API composition
  • transform composition
  • parser and deserializer contracts
  • HTML insertData
  • DnD-style contracts
• Grow the compile-only type lane here first:
  • plugin creation
  • editor creation
  • inference
  • option merging
  • API merging
• Port upstream Slate React invariants by behavior, not by file.
• When a core source test mounts Plate while the same run also loads public-package React entrypoints, treat duplicate-instance warnings as test noise. Suppress them in the test wrapper with suppressInstanceWarning instead of changing runtime warning logic.
• For provider-only React specs in core, reuse the shared packages/core/src/react/__tests__/TestPlate.tsx helper instead of re-declaring local const Plate = ... wrappers.

selection

• moveSelection and shiftSelection stay on Plate. They are genuinely Plate-bound exceptions, not cleanup debt.

docx, docx-io, and app integration

• Keep app-owned cross-package integration tests under apps/www/src/__tests__/package-integration.
• Keep buckets local under that folder instead of scattering app-owned integration coverage through src/lib.
• Package tests must not pull app aliases, app kits, or registries into package graphs.
• Fixture-heavy docx and docx-io suites are valid reasons to keep __tests__/.

slate

• Focus on pure editor, query, and transform behavior first.
• Keep runtime coverage on navigation, selection math, structural queries, transform edge cases, extension transforms, and createEditor legacy sync.
• Keep a small compile-only type lane for public @platejs/slate contracts.
• Use selective upstream mining. Pull invariants that cheaply improve local public-contract coverage; do not mirror upstream blindly.
• Add direct helper specs for custom Slate code when indirect coverage is lying.
• Use lcov as package truth. Bun’s text coverage summary is noisy for targeted package runs.
• Stop once the remaining misses are mostly deferred DOM wrappers plus low-risk non-DOM dust.
• Later utility and core work should mine these upstream slate-react invariants:
  • use-slate-selector: selector equality and stale-rerender prevention
  • use-slate: editor version and subscription behavior
  • use-selected: selection rerender and path stability
  • editable: value-change vs selection-change partitioning
  • decorations: decoration propagation and redecorate behavior
  • chunking: chunk or index invalidation only if remaining core gaps justify it
• Skip react-editor DOM focus coverage unless a real Plate bug forces it.
• Playwright example coverage stays out.

Reviewed Exceptions

createPlateEditor allowlist

Keep createPlateEditor when the contract is actually about:

• React or provider wiring
• rendered output or DOM behavior
• store rerender semantics
• Plate plugin conversion boundaries
• the known Plate-only selection APIs: moveSelection and shiftSelection

Do not treat these files as backlog just because they still use Plate.

__tests__/ allowlist

Keep __tests__/ when it holds:

• package-local helpers or fixture banks
• intentionally split multi-file suites like withAutoformat
• fixture-heavy integration suites like docx and docx-io
• app-owned cross-package integration suites under apps/www/src/__tests__/package-integration

Quick Reference

• Start with the smallest seam that proves the contract: createEditor -> createSlateEditor -> createPlateEditor.
• Work in passes: >= 6 first, rerun coverage, then worthwhile >= 5, then switch to architecture-safety targets.
• Use bun run test for the fast default loop. Use pnpm test:all for the full suite.
• Use bun run test:profile to inspect the fast loop and bun run test:slowest to enforce it.
• pnpm test:slowest has two bands: warning zone for local drift and hard CI failure thresholds. Fix the warning zone before it becomes a PR failure.
• Use Bun globals. Do not import them from bun:test.
• Keep specs beside the implementation. Use __tests__/ only for helpers, fixtures, or intentional split or integration suites.
• Use plain objects for simple state. Use JSX hyperscript only when tree or selection shape is the contract.
• Prefer explicit assertions. Use render-returned queries over screen, and use direct style-property assertions over toHaveStyle.
• Delete skips, commented tests, dead smoke tests, and stale snapshot files after broad title renames.
• Package tests must stay package-local. No app registries, no app kits, no cross-spec imports.
• For package-only coverage decisions, trust lcov, not Bun’s broad text summary.
• Keep exactly two lanes:
  • fast lane: *.spec.ts[x], run by pnpm test
  • slow lane: *.slow.ts[x], run by pnpm test:slow
• Use pnpm test:all for the full repo test run instead of relying on bare bun test.
• Stop before 100%. When the remaining misses are wrappers, DOM/provider dust, sludge, or crumbs, you are done.