feat: LLM-friendly output formats (TAP + JSON)

[ngarbezza]

Implements #380 — the first quick win of the AI roadmap (see doc/ai-ideas.md). Adds machine-readable output so an LLM agent (or any tool) can consume Testy's results with few tokens. Driver: simplicity as cost.

What's included

• Polymorphic Formatter family: a base Formatter (event protocol + protected helpers, no-op defaults) with three subclasses:
  • ConsoleFormatter — the existing human-readable colored output (default, unchanged).
  • TapFormatter — TAP version 13, streaming one line per test.
  • JsonFormatter — a single structured JSON object printed at the end.
• FormatterFactory selects the formatter; ConsoleUI wires it from configuration.output().
• Configuration surface: output key in .testyrc.json (default console) and -o/--output <console|tap|json> CLI flag, with validation. --help updated.
• Docs: README.md + README_es.md (config option, CLI flag, "machine-readable output" section).

Machine output is language-neutral (statuses/keys are not translated); only failure messages are localized to the configured language. AI lives entirely outside the core — zero new runtime dependencies.

Design / plan

• Design doc: doc/plans/2026-06-06-llm-friendly-output-design.md
• Implementation plan: doc/plans/2026-06-06-llm-friendly-output.md

Examples

npx testy -o tap
npx testy -o json

TAP:

TAP version 13
ok 1 - something is true
not ok 2 - sum works
  ---
  message: Expected 5 to be equal to 4
  at: tests/example_test.js:12
  severity: failure
  ---
1..2
# tests 2
# pass 1
# fail 1
...

JSON (single line): { "tool": "@pmoo/testy", "version": "...", "summary": { total, passed, failed, errored, pending, skipped, durationMs }, "suites": [ { name, file, tests: [ { name, status, failure? } ] } ] }

Testing

• TDD throughout; new tests for TAP, JSON, the factory, the config accessor, and the CLI flag (incl. the ordering fix + invalid-value rejection).
• Full suite: 405/405 passing; lint clean.
• End-to-end verified via the real CLI for -o tap, -o json, and default.

Known limitations / follow-ups (non-blocking)

• TAP failure message: collapses internal newlines to spaces (error stack traces become one line).
• An invalid output value coming from .testyrc.json (not the CLI) silently falls back to console, matching how language is handled today.
• displayError (top-level runtime errors during a run) is a no-op in TAP/JSON mode — machine consumers rely on the non-zero exit code; emitting a Bail out! / {"error":...} could be a follow-up.
• Nice-to-have tests: multi-suite JSON accumulation, explicit TAP stack-collapsing/# time assertions.

Closes #380.

🤖 Generated with Claude Code