Migrated tests to jest

Used jest-codemods to migrate, will have to pass everything by hand before we can merge.

test/stringPermutations/stringPermutations.js

@@ -1,11 +0,0 @@
-const stringPermutations = str => {
-if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
-return str
-.split('')
-.reduce(
-(acc, letter, i) =>
-acc.concat(stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
-[]
-);
-};
-module.exports = stringPermutations;