Updated the test system

test/negate.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {negate} = require('./_30s.js');
+
+test('negate is a Function', () => {
+  expect(negate).toBeInstanceOf(Function);
+});
+test('Negates a predicate function', () => {
+  expect([1, 2, 3, 4, 5, 6].filter(negate(n => n % 2 === 0))).toEqual([1, 3, 5]);
+});