Migrated tests to jest

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

test/invertKeyValues/invertKeyValues.js

@@ -1,8 +0,0 @@
-const invertKeyValues = (obj, fn) =>
-Object.keys(obj).reduce((acc, key) => {
-const val = fn ? fn(obj[key]) : obj[key];
-acc[val] = acc[val] || [];
-acc[val].push(key);
-return acc;
-}, {});
-module.exports = invertKeyValues;