ExUnitJSON

AI-friendly JSON test output for ExUnit.

ExUnitJSON provides structured JSON output from mix test for use with AI editors like Claude Code, Cursor, and other tools that benefit from machine-parseable test results.

Full Documentation on HexDocs

Features

Drop-in replacement for mix test with JSON output
AI-optimized default: Shows only failures (use --all for all tests)
Code coverage with --cover and coverage gating with --cover-threshold N
Detailed failure information with assertion values and stacktraces
Filtering: --summary-only, --first-failure, --filter-out, --group-by-error
File output: --output results.json
Deterministic test ordering for reproducible output
No runtime dependencies (uses Elixir 1.18+ built-in :json)

Installation

Add ex_unit_json to your list of dependencies in mix.exs:

def deps do
  [
    {:ex_unit_json, "~> 0.4.0", only: [:dev, :test], runtime: false}
  ]
end

Configure Mix to run test.json in the test environment:

def cli do
  [preferred_envs: ["test.json": :test]]
end

Usage

Recommended Workflow

# First run - see failures directly (default behavior)
mix test.json --quiet

# Iterate on failures (fast - only runs previously failed tests)
mix test.json --quiet --failed --first-failure

# Verify all failures fixed
mix test.json --quiet --failed --summary-only

# See all tests (when you need passing tests too)
mix test.json --quiet --all

Options

Flag	Description
`--quiet`	Suppress Logger output for clean JSON
`--all`	Include all tests (default shows only failures)
`--summary-only`	Output only the summary, no individual tests
`--first-failure`	Output only the first failed test
`--filter-out PATTERN`	Mark matching failures as filtered (repeatable)
`--group-by-error`	Group failures by similar error message
`--output FILE`	Write JSON to file instead of stdout
`--cover`	Enable code coverage
`--cover-threshold N`	Fail if coverage below N% (requires `--cover`)
`--no-warn`	Suppress the "use --failed" tip

All standard mix test flags are passed through (--failed, --only, --exclude, --seed, etc.).

Code Coverage

mix test.json --quiet --cover
mix test.json --quiet --cover --cover-threshold 80

Coverage output includes total percentage, per-module breakdown, and uncovered line numbers. See full documentation for schema details.

Using with jq

# Summary (MIX_QUIET=1 prevents compile output from breaking jq)
MIX_QUIET=1 mix test.json --quiet --summary-only | jq '.summary'

# Full details via file (avoids piping issues entirely)
mix test.json --quiet --output /tmp/results.json
jq '.tests[] | select(.state == "failed")' /tmp/results.json

Requirements

Elixir 1.18+ (uses built-in :json module)

License

MIT