lint-staged.config.js

'use strict';

const fs = require('fs');

module.exports = {
  '*.js': [
    'eslint --fix',
    (files) => {
      const tests = findTests(files);
      return tests.length ? `npm run test:files -- ${tests.join(' ')}` : 'echo';
    }
  ],
  '*.{js,css,md}': 'prettier --write'
};

function findTests(files) {
  const tests = new Set();
  files.forEach((file) => {
    if (file.endsWith('.test.js')) {
      tests.add(file);
      return;
    }
    const test = file.replace(/\.js$/, '.test.js');
    try {
      fs.accessSync(test); // eslint-disable-line node/no-sync
    } catch (e) {
      return;
    }
    tests.add(test);
  });
  return Array.from(tests);
}

{
  "scripts": {
    "test:files": "mocha -R dot -r ./test/fixture/assertions/*"
  },
  "husky": {
    "hooks": {
      "pre-commit": "lint-staged --relative"
    }
  }
}