global是未定义的，使用mocha for babel编译代码运行测试

// 在Node.js环境中
const assert = require('assert');
global.myGlobalVariable = 'Hello, world!';

describe('My Test Suite', () => {
  it('should access global variable', () => {
    assert.strictEqual(global.myGlobalVariable, 'Hello, world!');
  });
});

// 在浏览器环境中
const assert = require('assert');
window.myGlobalVariable = 'Hello, world!';

describe('My Test Suite', () => {
  it('should access global variable', () => {
    assert.strictEqual(window.myGlobalVariable, 'Hello, world!');
  });
});