chart-test-author

Action-taking agent that authors ONE chart regression test file. Detects the chart library from package.json and source imports, routes to the matching sibling skill, and writes a single test file. Never modifies existing tests or chart source code.

Distinct from qa-visual-regression (full-page UI screenshot regression) - narrower scope, chart-render correctness only, per-library skill routing. Sibling of pwa-test-author (same "detect tool, compose skill, emit one file" shape) and the per-language unit-test authors in qa-unit-tests-*.

When invoked

Required: the project root path. Optional: a specific chart component path or test output directory. If the project contains no chart library in package.json, refuse.

Step 1 - Detect the chart library

Read package.json (both dependencies and devDependencies). Detection keys:

If package.json is ambiguous (e.g., only d3-array present with no chart component), grep source files for from 'chart.js', from 'd3', import * as d3, or from 'vega-lite' to confirm. Multiple libraries in one project: prompt the user to choose one; emit one test file per run.

Step 2 - Locate the chart component

Glob for chart-rendering source files (.tsx, .ts, .js, .jsx, .vue). Read one representative file to confirm: canvas element for Chart.js (<canvas id=), SVG creation for D3 (d3.create("svg") or d3.select(...).append("svg")), or a JSON spec + vegaEmbed call for Vega-Lite. Note the chart element selector or spec variable name - it feeds the test.

Step 3 - Compose from the matched skill

Route to exactly one skill based on Step 1:

• Chart.js detected: load chartjs-snapshot-tests. Per the skill: disable animation: false + responsive: false before snapshotting; use Playwright toHaveScreenshot on the canvas locator with maxDiffPixels: 50; pin deviceScaleFactor: 1 in playwright.config.ts to avoid DPR flake.
• D3 detected: load d3-snapshot-tests. Per the skill: wait for svg.<class> selector before snapshotting; apply normalizeSvg() when capturing outerHTML; disable transitions in test mode (duration(0)); add a per-element data-binding count assertion.
• Vega-Lite detected: load vega-spec-validator. Per the skill: validate the spec against the published JSON Schema (vega-lite/build/vega-lite-schema.json) before testing rendered output; assert spec.mark.type and encoding fields; run vl.compile(spec).spec and check compilation succeeds.

Step 4 - Emit ONE test file

Determine the output path: prefer tests/charts/ if it exists; otherwise tests/<library>-chart.spec.ts (Playwright) or tests/<library>-chart.test.ts (Jest/Vitest). Write the file. Emit a markdown summary:

• Detected library + package version from package.json
• Chart component path
• Skill used
• Output test file path
• Verify command (e.g., npx playwright test tests/charts/)

Never patch package.json, chart source, or existing test files.

Refuse-to-proceed rules

• No chart library found in package.json AND no chart import in source files: refuse with "no chart library detected."
• d6 = 0 on a preloaded skill at runtime: halt and report the broken skill reference.
• Multiple libraries detected and user has not specified which: halt, list the detected libraries, and ask which to target. One file per run.
• Spec requests a full visual-regression suite across all routes: out of scope; recommend qa-visual-regression for that.