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1# Mocking Request2 3Undici has its own mocking [utility](../api/MockAgent.md). It allow us to intercept undici HTTP requests and return mocked values instead. It can be useful for testing purposes.4 5Example:6 7```js8// bank.mjs9import { request } from 'undici'10 11export async function bankTransfer(recipient, amount) {12  const { body } = await request('http://localhost:3000/bank-transfer',13    {14      method: 'POST',15      headers: {16        'X-TOKEN-SECRET': 'SuperSecretToken',17      },18      body: JSON.stringify({19        recipient,20        amount21      })22    }23  )24  return await body.json()25}26```27 28And this is what the test file looks like:29 30```js31// index.test.mjs32import { strict as assert } from 'assert'33import { MockAgent, setGlobalDispatcher, } from 'undici'34import { bankTransfer } from './bank.mjs'35 36const mockAgent = new MockAgent();37 38setGlobalDispatcher(mockAgent);39 40// Provide the base url to the request41const mockPool = mockAgent.get('http://localhost:3000');42 43// intercept the request44mockPool.intercept({45  path: '/bank-transfer',46  method: 'POST',47  headers: {48    'X-TOKEN-SECRET': 'SuperSecretToken',49  },50  body: JSON.stringify({51    recipient: '1234567890',52    amount: '100'53  })54}).reply(200, {55  message: 'transaction processed'56})57 58const success = await bankTransfer('1234567890', '100')59 60assert.deepEqual(success, { message: 'transaction processed' })61 62// if you dont want to check whether the body or the headers contain the same value63// just remove it from interceptor64mockPool.intercept({65  path: '/bank-transfer',66  method: 'POST',67}).reply(400, {68  message: 'bank account not found'69})70 71const badRequest = await bankTransfer('1234567890', '100')72 73assert.deepEqual(badRequest, { message: 'bank account not found' })74```75 76Explore other MockAgent functionality [here](../api/MockAgent.md)77 78## Debug Mock Value79 80When 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()`:81 82```js83const mockAgent = new MockAgent();84 85setGlobalDispatcher(mockAgent);86mockAgent.disableNetConnect()87 88// Provide the base url to the request89const mockPool = mockAgent.get('http://localhost:3000');90 91mockPool.intercept({92  path: '/bank-transfer',93  method: 'POST',94}).reply(200, {95  message: 'transaction processed'96})97 98const badRequest = await bankTransfer('1234567890', '100')99// Will throw an error100// MockNotMatchedError: Mock dispatch not matched for path '/bank-transfer':101// subsequent request to origin http://localhost:3000 was not allowed (net.connect disabled)102```103 104## Reply with data based on request105 106If the mocked response needs to be dynamically derived from the request parameters, you can provide a function instead of an object to `reply`:107 108```js109mockPool.intercept({110  path: '/bank-transfer',111  method: 'POST',112  headers: {113    'X-TOKEN-SECRET': 'SuperSecretToken',114  },115  body: JSON.stringify({116    recipient: '1234567890',117    amount: '100'118  })119}).reply(200, (opts) => {120  // do something with opts121 122  return { message: 'transaction processed' }123})124```125 126in this case opts will be127 128```129{130  method: 'POST',131  headers: { 'X-TOKEN-SECRET': 'SuperSecretToken' },132  body: '{"recipient":"1234567890","amount":"100"}',133  origin: 'http://localhost:3000',134  path: '/bank-transfer'135}136```137