如何对其接口定义在子模块中的函数进行单元测试

// 假设有一个模块 `api.js`，其中定义了一个函数 `fetchData`
// api.js
export async function fetchData(url) {
  const response = await fetch(url);
  return response.json();
}

// 测试文件 `api.test.js`
import { fetchData } from './api';
import fetch from 'node-fetch';

jest.mock('node-fetch');

test('fetchData should return correct data', async () => {
  const mockData = { message: 'Hello, World!' };
  fetch.mockResolvedValueOnce({
    json: jest.fn().mockResolvedValueOnce(mockData)
  });

  const result = await fetchData('https://example.com/api');
  expect(result).toEqual(mockData);
});

test('fetchData should handle empty URL', async () => {
  await expect(fetchData('')).rejects.toThrow();
});

test('fetchData should handle large URL', async () => {
  const longUrl = 'a'.repeat(10000);
  await expect(fetchData(longUrl)).rejects.toThrow();
});

test('fetchData should handle fetch error', async () => {
  fetch.mockRejectedValueOnce(new Error('Network error'));
  await expect(fetchData('https://example.com/api')).rejects.toThrow('Network error');
});