Updated the test system

test/byteSize.test.js

@@ -0,0 +1,22 @@
+const expect = require('expect');
+const Blob = class {
+  constructor(s) {
+    return {
+      size: Buffer.byteLength(s.toString())
+    };
+  }
+};
+const byteSize = str => new Blob([str]).size;
+
+test('byteSize is a Function', () => {
+  expect(byteSize).toBeInstanceOf(Function);
+});
+test('Works for a single letter', () => {
+  expect(byteSize('a')).toBe(1);
+});
+test('Works for a common string', () => {
+  expect(byteSize('Hello World')).toBe(11);
+});
+test('Works for emoji', () => {
+  expect(byteSize('😀')).toBe(4);
+});