How do I test asynchronous code in JavaScript?

How do I test asynchronous code in JavaScript?

You can use testing frameworks like Jest or Mocha along with async/await or Promises to test asynchronous code.

Can you give me an example using Jest?

Sure! Here's a simple example:

// async function to be tested
const fetchData = async () => {
    const response = await fetch('https://api.example.com/data');
    return response.json();
};

// test case
test('fetches data from API', async () => {
    const data = await fetchData();
    expect(data).toBeDefined();
});

What if I want to test error handling?

You can use Jest's rejects method to test for errors. Here's an example:

// async function that throws an error
const fetchDataWithError = async () => {
    throw new Error('Network error');
};

// test case for error handling
test('fetches data and handles error', async () => {
    await expect(fetchDataWithError()).rejects.toThrow('Network error');
});