Updated the test system

test/transform.test.js

@@ -0,0 +1,18 @@
+const expect = require('expect');
+const {transform} = require('./_30s.js');
+
+test('transform is a Function', () => {
+  expect(transform).toBeInstanceOf(Function);
+});
+test('Transforms an object', () => {
+  expect(
+    transform(
+      { a: 1, b: 2, c: 1 },
+      (r, v, k) => {
+        (r[v] || (r[v] = [])).push(k);
+        return r;
+      },
+      {}
+    )
+  ).toEqual({ '1': ['a', 'c'], '2': ['b'] });
+});