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

test/truncateString/truncateString.js

@@ -1,2 +1,2 @@
-module.exports = (str, num) =>
+module.exports = truncateString = (str, num) =>
 str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;