generate new test that did already exist & update all module snippets with declaration

test/promisify/promisify.js

@@ -1,4 +1,4 @@
-module.exports = func => (...args) =>
+module.exports = promisify = func => (...args) =>
 new Promise((resolve, reject) =>
 func(...args, (err, result) => (err ? reject(err) : resolve(result)))
 );