Updated the test system

test/call.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {call} = require('./_30s.js');
+
+test('call is a Function', () => {
+  expect(call).toBeInstanceOf(Function);
+});
+test('Calls function on given object', () => {
+  expect(call('map', x => x * 2)([1, 2, 3])).toEqual([2, 4, 6]);
+});