tap-arc

tap-arc 📋

A small TAP reporter with spec-like output, streaming, and failure diffing.
tap-arc on npmjs.org »

Contents: Install • Development • FAQ

Objectives

• minimal, informative spec-like output for all assertions
• minimal, maintained dependencies
• streaming in and out
• helpful diffing for failures

Installation and Usage

Compatible with Node.js v16+ -- v14 also works but is not recommended.

Save tap-arc as a development dependency:

npm i -D tap-arc

Simply pipe tap output to tap-arc.
Example npm test script:

// package.json
"scripts": {
  "test": "tape test/**/*.js | tap-arc"
}

💁 tap-arc will format output from any tap reporter. tape is our favorite and was used for testing.

tap-arc --help

Usage:
  tap-arc <options>

Parses TAP data from stdin, and outputs a "spec-like" formatted result.

Options:

  -v | --verbose
    Output full stack trace, TAP version, and plan

  -p | --pessimistic | --bail
    Immediately exit upon encountering a failure
    example: tap-arc -p

  --no-diff
    Do not show diff for failed assertions
    example: tap-arc --no-diff

  --no-color
    Output without ANSI escape sequences for colors
    example: tap-arc --no-color

  --fail-bad-count
    Fail when the number of assertions parsed does not match the plan
    example: tap-arc --fail-bad-count

Development

When building tap-arc, it's helpful to try various TAP outputs. See package.json "scripts" for useful "tap-arc.*" commands to test passing and failing TAP.

npm run tap-arc.simple # used to create the screen shot above

Dev Tips

1. ./test/smoke.js contains the bare minimum usage of tap-parser with process.stdin.
   Helpful for understanding tap-parser's behavior.

2. To see previous exit code, run:

echo $?

Testing

Primarily, tap-arc is tested to output the correct exit code based on your test suite's TAP output.

Testing could be improved by unit testing the printer and diff maker.

FAQ

"Expected n assertions, but found < n"

What happened?
✅ The TAP parser found zero failing tests
✅ The final tally from the raw TAP shows n of n passed
🤨 But the TAP plan called for more assertions than were found, counted, and parsed.

💁‍♀️ Currently, when this case is detected, tap-arc will exit with a successful status code.
This can be overridden with the --fail-bad-count flag.

Why, though?
This has been observed specifically on Windows, where the TAP output is buffered to another stream and not piped to tap-arc.
Libraries like mock-fs tinker with stdout and subsequent TAP output is lost. Try closing those helpers before making an assertion that generates TAP.

"0 tests found" fails the suite?

Yes. At least one passing test is required to pass the suite.
This helps ensures there wasn't a silent, catastrophic failure in the test suite.

Why does tap-arc get to decide these things?

tap-arc is responsible for the test suite's exit code. If your entire CI stack is piped to a reporter, it's an important job. So tap-arc is a bit skeptical by default to help ensure your suite is passing.

If you'd like to see different behavior from tap-arc, please open an issue or PR. We'd love to hear your use case.

Credit & Inspiration

• tap-spec ol' reliable, but a bit stale and vulnerable
• tap-difflet inspired output and diffing, also vulnerable
• tap-min helpful approaches to streaming and exit codes, used to report tap-arc's TAP