Updated the test system

test/invertKeyValues.test.js

@@ -0,0 +1,15 @@
+const expect = require('expect');
+const {invertKeyValues} = require('./_30s.js');
+
+test('invertKeyValues is a Function', () => {
+  expect(invertKeyValues).toBeInstanceOf(Function);
+});
+test("invertKeyValues({ a: 1, b: 2, c: 1 }) returns { 1: [ 'a', 'c' ], 2: [ 'b' ] }", () => {
+  expect(invertKeyValues({ a: 1, b: 2, c: 1 })).toEqual({ 1: ['a', 'c'], 2: ['b'] });
+});
+test("invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value) returns { group1: [ 'a', 'c' ], group2: [ 'b' ] }", () => {
+  expect(invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value)).toEqual({
+    group1: ['a', 'c'],
+    group2: ['b']
+  });
+});