jest_async_await_testing_quickstart_with_promises.ts

1// Function to be tested (usually in a separate file like fetchData.ts)
2export const fetchData = (): Promise<string> => {
3  return new Promise((resolve) => {
4    setTimeout(() => {
5      resolve('peanut butter');
6    }, 100);
7  });
8};
9
10// Test file (fetchData.test.ts)
11import { fetchData } from './fetchData';
12
13test('the data is peanut butter', async () => {
14  const data = await fetchData();
15  expect(data).toBe('peanut butter');
16});
17
18test('the fetch fails with an error', async () => {
19  expect.assertions(1);
20  try {
21    await fetchData();
22  } catch (e) {
23    expect(e).toMatch('error');
24  }
25});