Migrated tests to jest

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

test/symmetricDifferenceBy/symmetricDifferenceBy.js

@@ -1,6 +0,0 @@
-const symmetricDifferenceBy = (a, b, fn) => {
-const sA = new Set(a.map(v => fn(v))),
-sB = new Set(b.map(v => fn(v)));
-return [...a.filter(x => !sB.has(fn(x))), ...b.filter(x => !sA.has(fn(x)))];
-};
-module.exports = symmetricDifferenceBy;