Undici has its own mocking utility. It allow us to intercept undici HTTP requests and return mocked values instead. It can be useful for testing purposes.
Example:
// bank.mjs import { request } from 'undici' export async function bankTransfer(recipient, amount) { const { body } = await request('http://localhost:3000/bank-transfer', { method: 'POST', headers: { 'X-TOKEN-SECRET': 'SuperSecretToken', }, body: JSON.stringify({ recipient, amount }) } ) return await body.json() }
And this is what the test file looks like:
// index.test.mjs import { strict as assert } from 'assert' import { MockAgent, setGlobalDispatcher, } from 'undici' import { bankTransfer } from './bank.mjs' const mockAgent = new MockAgent(); setGlobalDispatcher(mockAgent); // Provide the base url to the request const mockPool = mockAgent.get('http://localhost:3000'); // intercept the request mockPool.intercept({ path: '/bank-transfer', method: 'POST', headers: { 'X-TOKEN-SECRET': 'SuperSecretToken', }, body: JSON.stringify({ recipient: '1234567890', amount: '100' }) }).reply(200, { message: 'transaction processed' }) const success = await bankTransfer('1234567890', '100') assert.deepEqual(success, { message: 'transaction processed' }) // if you dont want to check whether the body or the headers contain the same value // just remove it from interceptor mockPool.intercept({ path: '/bank-transfer', method: 'POST', }).reply(400, { message: 'bank account not found' }) const badRequest = await bankTransfer('1234567890', '100') assert.deepEqual(badRequest, { message: 'bank account not found' })
Explore other MockAgent functionality here
When the interceptor and the request options are not the same, undici will automatically make a real HTTP request. To prevent real requests from being made, use mockAgent.disableNetConnect()
:
const mockAgent = new MockAgent(); setGlobalDispatcher(mockAgent); mockAgent.disableNetConnect() // Provide the base url to the request const mockPool = mockAgent.get('http://localhost:3000'); mockPool.intercept({ path: '/bank-transfer', method: 'POST', }).reply(200, { message: 'transaction processed' }) const badRequest = await bankTransfer('1234567890', '100') // Will throw an error // MockNotMatchedError: Mock dispatch not matched for path '/bank-transfer': // subsequent request to origin http://localhost:3000 was not allowed (net.connect disabled)
If the mocked response needs to be dynamically derived from the request parameters, you can provide a function instead of an object to reply
:
mockPool.intercept({ path: '/bank-transfer', method: 'POST', headers: { 'X-TOKEN-SECRET': 'SuperSecretToken', }, body: JSON.stringify({ recipient: '1234567890', amount: '100' }) }).reply(200, (opts) => { // do something with opts return { message: 'transaction processed' } })
in this case opts will be
{ method: 'POST', headers: { 'X-TOKEN-SECRET': 'SuperSecretToken' }, body: '{"recipient":"1234567890","amount":"100"}', origin: 'http://localhost:3000', path: '/bank-transfer' }