Updated the test system

test/intersection.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {intersection} = require('./_30s.js');
+
+test('intersection is a Function', () => {
+  expect(intersection).toBeInstanceOf(Function);
+});
+test('Returns a list of elements that exist in both arrays', () => {
+  expect(intersection([1, 2, 3], [4, 3, 2])).toEqual([2, 3]);
+});