ValidationFileChanged· *.ts|*.tsx|*.js|*.jsx

Auto-run tests when source files change

Triggers the project test suite asynchronously whenever a watched source file changes on disk. Results are injected as context for Claude on the next turn, so Claude can react to test failures without being explicitly asked.

Use cases

Continuously validate that external file changes don't break tests during a session
Automatically surface test regressions when hot-reloading tools modify source files
Keep Claude informed of test status after every file system change

Providers & tags

Claude Code

#tests#file-watch#ci#async#validation

settings.json fragment

{
  "hooks": {
    "FileChanged": [
      {
        "hooks": [
          {
            "async": true,
            "command": "node $CLAUDE_PROJECT_DIR/.claude/hooks/file-changed-run-tests.mjs",
            "timeout": 120,
            "type": "command"
          }
        ],
        "matcher": "*.ts|*.tsx|*.js|*.jsx"
      }
    ]
  }
}

Script · .claude/hooks/file-changed-run-tests.mjs

#!/usr/bin/env node
// Relance les tests quand un fichier change (FileChanged)
import { readFileSync } from 'fs';
import { execSync } from 'child_process';
import { fileURLToPath } from 'url';

function defaultExec(cmd) {
  return execSync(cmd, { timeout: 90_000 });
}

export function run(input, { exec = defaultExec } = {}) {
  if (input.event === 'unlink') return null;

  try {
    const out = exec('npm test --if-present 2>&1').toString();
    return {
      hookSpecificOutput: {
        hookEventName: 'FileChanged',
        additionalContext: `Tests passed after ${input.file_path} changed.\n${out.slice(-500)}`,
      },
    };
  } catch (e) {
    const out = (e.stdout ?? e.stderr ?? e.message).toString().slice(0, 1000);
    return {
      hookSpecificOutput: {
        hookEventName: 'FileChanged',
        additionalContext: `Tests FAILED after ${input.file_path} changed:\n${out}`,
      },
    };
  }
}

/* v8 ignore next 5 */
if (process.argv[1] === fileURLToPath(import.meta.url)) {
  const input = JSON.parse(readFileSync(0, 'utf8'));
  const result = run(input);
  if (result) process.stdout.write(JSON.stringify(result));
}