如何测试类列表。使用Jest添加/删除?

index.ts :

export const toggleClass = (elementDOM, className) => {
  if (elementDOM.classList.contains(className)) {
    elementDOM.classList.remove(className);
  } else {
    elementDOM.classList.add(className);
  }
};

index.spec.ts :

import { toggleClass } from '.';

describe('toggleClass', () => {
  const mockedElementDOM = { classList: { contains: jest.fn(), remove: jest.fn(), add: jest.fn() } };

  it('should remove the class', () => {
    const className = 'a';
    mockedElementDOM.classList.contains.mockReturnValueOnce(true);
    toggleClass(mockedElementDOM, className);
    expect(mockedElementDOM.classList.remove).toBeCalledWith('a');
  });

  it('should add the class', () => {
    const className = 'a';
    mockedElementDOM.classList.contains.mockReturnValueOnce(false);
    toggleClass(mockedElementDOM, className);
    expect(mockedElementDOM.classList.add).toBeCalledWith('a');
  });
});

 PASS  src/stackoverflow/45918386/index.spec.ts
  toggleClass
    ✓ should remove the class (4ms)
    ✓ should add the class (1ms)

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.ts |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        3.575s, estimated 9s

源代码: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/45918386