# Mocking Request
Undici 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.
Example:
```js
// 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:
```js
// 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](../api/MockAgent.md)
## Debug Mock Value
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()`:
```js
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)
```
## Reply with data based on request
If the mocked response needs to be dynamically derived from the request parameters, you can provide a function instead of an object to `reply`:
```js
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'
}
```
