How to Build a DIY Quality Gate in CI With Scripts

A DIY gate is a script that reads coverage and complexity outputs and exits non-zero when a threshold is crossed.

Many tools have a built-in threshold flag (Jest coverageThreshold, pytest-cov --cov-fail-under). For anything else, parse the report in a small script and exit 1 when it fails.

Built-in coverage gate

jobs:
  gate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm ci
      - run: npx jest --coverage --coverageThreshold='{"global":{"lines":80,"branches":70}}'

Script gate on a JSON summary

#!/usr/bin/env bash
set -euo pipefail
PCT=$(jq '.total.lines.pct' coverage/coverage-summary.json)
echo "line coverage: $PCT%"
awk "BEGIN { exit ($PCT < 80) ? 1 : 0 }" \
  || { echo "coverage below 80%"; exit 1; }

Gotchas

• Use the tool built-in threshold when it exists; it is less brittle than parsing a report format.
• Emit the summary reporter (e.g. --coverageReporters=json-summary) so the script has structured input.

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