Run tests after file changes

This hook starts a test suite in the background whenever Claude writes a file, then reports the results back to Claude when the tests finish. Save this script to .claude/hooks/run-tests-async.sh in your project and make it executable with chmod +x:

#!/bin/bash
# run-tests-async.sh

# Read hook input from stdin
INPUT=$(cat)
FILE_PATH=$(echo "$INPUT" | jq -r '.tool_input.file_path // empty')

# Only run tests for source files
if [[ "$FILE_PATH" != *.ts && "$FILE_PATH" != *.js ]]; then
  exit 0
fi

# Run tests and report results to Claude via additionalContext
RESULT=$(npm test 2>&1)
EXIT_CODE=$?

if [ $EXIT_CODE -eq 0 ]; then
  MSG="Tests passed after editing $FILE_PATH"
else
  MSG="Tests failed after editing $FILE_PATH: $RESULT"
fi
jq -nc --arg msg "$MSG" '{hookSpecificOutput: {hookEventName: "PostToolUse", additionalContext: $msg}}'

Then add this configuration to .claude/settings.json in your project root. The async: true flag lets Claude keep working while tests run:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PROJECT_DIR}/.claude/hooks/run-tests-async.sh",
            "args": [],
            "async": true
          }
        ]
      }
    ]
  }
}