Test migration to jest by hand

Apparently using regular expressions is way easier.

test/fromCamelCase/fromCamelCase.js

@@ -0,0 +1,6 @@
+const fromCamelCase = (str, separator = '_') =>
+str
+.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
+.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
+.toLowerCase();
+module.exports = fromCamelCase;