smallest-check-ladder

Smallest-Check Ladder (L0 -> L3)

Pick the smallest rung that could still falsify the change, run it for real, and escalate only when the rung passes and you need broader confidence. The point is to make "I ran the relevant tests" a concrete, reproducible command — not a vibe — while staying proportionate to the size of the diff.

Deterministic only. Every selector on this ladder chooses tests from a dependency graph or a coverage map (a fact about the code), never from a learned model that predicts which tests are "probably" relevant. ML predictive test selection is explicitly out of scope: it can silently drop a test that actually covers the change, which defeats the purpose of the rung.

The ladder

Rung	Scope	Cost	Run when
L0	Lint / typecheck the edited file(s) only	~1s	Every save. Always cheap enough to skip nothing.
L1	Impacted tests — the tests that exercise the changed files	seconds–low tens of s	Default for any code change before claiming "tests pass".
L2	Full suite (+ coverage)	minutes	L1 passed and the change is cross-cutting, or before a PR / task-completion gate.
L3	E2E against the built/packaged artifact	minutes+	Packaging, wiring, or user-journey surface touched (see packaged-artifact smoke gate).

Climb from the lowest rung that can catch this class of defect. A one-line pure-function fix rarely needs L3; a change to the Electron main process or the ffmpeg argv builder does.

Concrete commands

Substitute the actual changed paths for <files>.

L0 — edited-file lint / typecheck

# Python (Reframe: ruff + basedpyright)
ruff check <files>
basedpyright <files>

# TypeScript (Reframe app/)
npx tsc --noEmit               # project-wide but fast; or eslint just the files:
npx eslint <files>

L1 — impacted tests (deterministic selectors)

# Python — pytest-testmon: selects tests whose recorded coverage touches the changed code.
#   Deterministic: it replays a stored per-test coverage map, it does not predict.
#   Prerequisite (one-time): pip install pytest-testmon   # the --testmon flag is absent until installed
pytest --testmon                       # uses the .testmondata db built on the prior run
pytest --testmon-noselect <files>      # first run / to (re)seed the db for these files

# JavaScript/TypeScript — dependency-graph selection (deterministic: static import graph)
npx jest --findRelatedTests <files>    # jest projects
npx vitest related <files> --run       # vitest projects (Reframe app/ uses vitest)

--testmon needs its .testmondata db seeded once (run the suite under testmon, or use --testmon-noselect); if the db is stale or missing it falls back to running everything, so treat a suspiciously-large L1 selection as "seed first, then reselect".

L2 — full suite (always via longrun; it exceeds 60s)

# Wrap in longrun per the >60s rule; never a blocking foreground call.
~/source/agent-skills-toolchain/scripts/longrun.ps1 -Id l2-full -HangTimeoutSec 300 \
  -Cmd pytest --cov --cov-report=term-missing
# TS:
~/source/agent-skills-toolchain/scripts/longrun.ps1 -Id l2-vitest -HangTimeoutSec 300 \
  -Cmd npx vitest run --coverage

Coverage thresholds are not decided here — .coverage-thresholds.json remains the single source of truth and its enforcement command is the blocking gate. L2 just runs the suite.

L3 — e2e against the built artifact

# Run the project's e2e journeys against the packaged deliverable, not the source tree.
npx vitest run --config vitest.e2e.config.ts     # Reframe DOM e2e
# packaged smoke: _electron.launch({executablePath}) / pip install dist/*.whl in a fresh venv

Diff-scoped coverage (optional, orthogonal)

# "Did the lines I changed get exercised?" — deterministic, reads coverage.xml vs the diff.
diff-cover coverage.xml --compare-branch=main

How to use it in a turn

1. Identify the changed files.
2. Run L0 on them. Fix lint/type errors first — they invalidate any test result below.
3. Run L1 (--testmon / related). Capture the actual pass/fail output as evidence.
4. If the change is cross-cutting or you are about to claim task-complete / open a PR, climb to L2 (via longrun) and check .coverage-thresholds.json.
5. If packaging / wiring / a user journey changed, climb to L3.
6. Report the highest rung you ran and its real output — SUCCESS:<id> L1 12 passed / FAILED:<id> L1 2 failed …. Never claim "tests pass" from L0 alone.

Honesty rails

• A green rung is not a green suite. L1 asserts only "the impacted tests pass". If you claim the change is verified, name the rung you actually reached. A cross-cutting change verified only at L1 is under-verified — say so.
• Selector fallback is a silent widener, not a narrower. testmon with a missing db and related with an empty match both tend to run more (or, for related, nothing) — inspect the selected count; an empty L1 selection means "seed the db / check the path globs", never "there's nothing to run, ship it".
• No ML selection. If a tool proposes "predicted relevant tests" from a model, do not use it on this ladder — it can drop a covering test and manufacture a false green.

Scope / non-goals

• Does not author tests — that is tdd-workflow / test-driven-development (write the test first, watch it fail). This ladder only selects and runs existing tests.
• Does not own coverage thresholds — .coverage-thresholds.json does.
• Pairs with two-tier-verify, the same split stated as a decision rule: its INNER loop (after every edit) is L0+L1 here, its OUTER loop (once, at the commit boundary) is L2+L3. Go there for when to run which tier and its jest/vitest/pytest recipes; stay here for the rung commands and the selector caveats.
• Deferred (handBuild): wiring the concrete L1 command into ClaimWarningModule / claim_warning so a "tests pass" claim is auto-annotated with (or checked against) the smallest-check command that was actually run. That integration ships separately and, per council C5, in shadow mode (observe/annotate only — never blocks, never nags). This skill is the deterministic-command reference it will point at.

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Evidence: gem-hunt-2026-07-12 MASTER decision queue, A-Tier2 "Smallest-check ladder L0->L3 (testmon / jest-related / diff-cover)", verification-gates streams #4/#5. Additive doc; ships no gate. Deterministic dependency/coverage-map selectors only.