Evidence Driven Testing Agent Skill

Evidence-Driven Testing

Record annotated proof of behavior, then attach it to the PR and tracker issue.

Inputs

• Test targets (required): The behaviors/flows to verify, phrased as testable statements.
• PR / issue (optional): Where to post the evidence. If omitted, deliver to the requester only.

Instructions

1. Prepare the screen

• Maximize the browser/app window; close popups, notifications, and extra panels.
• Navigate to the starting state (logged in, correct page) BEFORE recording, unless setup itself is under test.

2. Start recording

• Begin the screen recording before the first meaningful action.
• Add a setup annotation describing the starting context, e.g. "Logged in, navigating to connectors page".

3. Annotate as you test

• At each named test's start, add a test_start annotation in Jest style: It should execute the tool directly when permission is 'always'.
• After each check, add an assertion annotation with result passed, failed, or untested.
• Rules for assertions:
• One assertion per meaningful state change — consolidate, don't annotate per UI label.
• Use "Precondition: ..." assertions to establish starting state.
• Keep under ~80 characters, high-signal.
• If a test cannot run (missing prerequisite, expired auth window), mark it untested with the reason — never skip silently.

4. Stop and review

• Stop recording after the final assertion.
• Confirm the recording captured the key moments before sharing.

5. Post the evidence

• Write a short report: what was tested, environment + exact commit, pass/fail per test, caveats.
• Post the video + summary as a PR comment (embed in the PR description if it's your PR).
• Attach the same video to the tracker issue (Linear/Jira) with a one-line result.
• Send the report + recording to the requester.

Guardrails

• Never record a half-covered or tiled window — maximize first.
• When verifying a fix, show or reference the old failure alongside the new success.
• Always state the exact commit/branch/deployment tested against.

Headless path (no GUI available)

When the agent has no desktop to record, keep the same assertion discipline;

swap the recorder for scripted capture:

• Save everything to .artifacts/<task-name>/ (gitignore it — evidence gets

uploaded, never committed). Keep the capture script beside the captures so

the run is repeatable.

• Screenshots: the before-and-after CLI (@vercel/before-and-after)

captures URLs or elements and its pairs feed PR embeds directly. In

containers/VMs where Chrome fails with "No usable sandbox", set

AGENT_BROWSER_ARGS="--no-sandbox".

• Video / multi-step flows: a one-off Playwright script, run without

adding playwright to the project's dependencies:

  npx --yes --package=playwright node record.mjs

(Plain npx playwright node record.mjs fails — node is not a Playwright

CLI command; --package=playwright is what puts the module on the path.)

Minimal record.mjs:

  import { chromium } from "playwright";
  const browser = await chromium.launch();
  const context = await browser.newContext({
    recordVideo: { dir: ".artifacts/<task-name>/" },
  });
  const page = await context.newPage();
  await page.goto("http://localhost:3000/path-under-test");
  // ...drive the flow, one meaningful state change per step...
  await context.close(); // finalizes the .webm
  await browser.close();

Trim or compress with ffmpeg if the file is large.

• The annotation protocol becomes files: number captures in test order

with the assertion in the name — 01-precondition-signed-in.png,

02-it-saves-on-blur-passed.png — and keep an assertions.md in the

artifacts folder listing each test_start / assertion with its result

(passed / failed / untested + reason).

Non-UI changes still need evidence

• API / performance: a scripted probe with measured numbers — request

counts per phase, latency before/after — captured to probe-output.txt.

• Rendering / canvas / shader: rendered frames plus pixel assertions

(diff values), reviewed by eye and saved as PNGs.

• Agent behavior: the relevant transcript excerpt showing the tool call

and response.

• Bug fixes: reproduce and capture the failure before writing the

fix — that capture is the "before" half of a before/after pair.

Capture hygiene

• Confirm the server you're probing is running *your* code (right port,

right process), especially when multiple agents share a machine:

lsof -i :<port> — or where lsof isn't installed,

ss -ltnp "sport = :<port>" to find the listener's PID, then

ps -p <pid> -o args= to confirm it's yours.

• Evidence complements the repo's checks (typecheck/build/tests); it never

replaces them.

• Hand before/after media pairs to a before/after tool for the PR embed

(e.g. before-and-after before.png after.png --markdown).