6.9 KiB
Mock Responses
Mocks give you full control over the response headers and body returned to the client. They can be used to return anything from a simple html string to a resourceful REST API. Typically, they're used to mock services but can be used for anything.
In the config, define an array called mocks. Each mock definition maps a route to a response. A simple home page:
{
"mocks": [
{
"route": "/",
"response": {
"body": "<h1>Welcome to the Mock Responses example</h1>"
}
}
]
}
Under the hood, the property values from the response object are written onto the underlying koa response object. You can set any valid koa response properies, for example type:
{
"mocks": [
{
"route": "/",
"response": {
"type": "text/plain",
"body": "<h1>Welcome to the Mock Responses example</h1>"
}
}
]
}
Conditional Response
To define a conditional response, set a request object on the mock definition. The request value acts as a query - the response defined will only be returned if each property of the request query matches. For example, return an XML response only if the request headers include accept: application/xml, else return 404 Not Found.
{
"mocks": [
{
"route": "/two",
"request": { "accepts": "xml" },
"response": {
"body": "<result id='2' name='whatever' />"
}
}
]
}
Multiple Potential Responses
To specify multiple potential responses, set an array of mock definitions to the responses property. The first response with a matching request query will be sent. In this example, the client will get one of two responses depending on the request method:
{
"mocks": [
{
"route": "/three",
"responses": [
{
"request": { "method": "GET" },
"response": {
"body": "<h1>Mock response for 'GET' request on /three</h1>"
}
},
{
"request": { "method": "POST" },
"response": {
"status": 400,
"body": { "message": "That method is not allowed." }
}
}
]
}
]
}
Dynamic Response
The examples above all returned static data. To define a dynamic response, create a mock module. Specify its path in the module property:
{
"mocks": [
{
"route": "/four",
"module": "/mocks/stream-self.js"
}
]
}
Here's what the stream-self module looks like. The module should export a mock definition (an object, or array of objects, each with a response and optional request). In this example, the module simply streams itself to the response but you could set body to any valid value.
const fs = require('fs')
module.exports = {
response: {
body: fs.createReadStream(__filename)
}
}
Response function
For more power, define the response as a function. It will receive the koa context as its first argument. Now you have full programmatic control over the response returned.
module.exports = {
response: function (ctx) {
ctx.body = '<h1>I can do anything i want.</h1>'
}
}
If the route contains tokens, their values are passed to the response. For example, with this mock...
{
"mocks": [
{
"route": "/players/:id",
"module": "/mocks/players.js"
}
]
}
...the id value is passed to the response function. For example, a path of /players/10?name=Lionel would pass 10 to the response function. Additional, the value Lionel would be available on ctx.query.name:
module.exports = {
response: function (ctx, id) {
ctx.body = `<h1>id: ${id}, name: ${ctx.query.name}</h1>`
}
}
RESTful Resource example
Here's an example of a REST collection (users). We'll create two routes, one for actions on the resource collection, one for individual resource actions.
{
"mocks": [
{ "route": "/users", "module": "/mocks/users.js" },
{ "route": "/users/:id", "module": "/mocks/user.js" }
]
}
Define a module (users.json) defining seed data:
[
{ "id": 1, "name": "Lloyd", "age": 40, "nationality": "English" },
{ "id": 2, "name": "Mona", "age": 34, "nationality": "Palestinian" },
{ "id": 3, "name": "Francesco", "age": 24, "nationality": "Italian" }
]
The collection module:
const users = require('./users.json')
/* responses for /users */
const mockResponses = [
/* Respond with 400 Bad Request for PUT and DELETE - inappropriate on a collection */
{ request: { method: 'PUT' }, response: { status: 400 } },
{ request: { method: 'DELETE' }, response: { status: 400 } },
{
/* for GET requests return a subset of data, optionally filtered on 'minAge' and 'nationality' */
request: { method: 'GET' },
response: function (ctx) {
ctx.body = users.filter(user => {
const meetsMinAge = (user.age || 1000) >= (Number(ctx.query.minAge) || 0)
const requiredNationality = user.nationality === (ctx.query.nationality || user.nationality)
return meetsMinAge && requiredNationality
})
}
},
{
/* for POST requests, create a new user and return the path to the new resource */
request: { method: 'POST' },
response: function (ctx) {
const newUser = ctx.request.body
users.push(newUser)
newUser.id = users.length
ctx.status = 201
ctx.response.set('Location', `/users/${newUser.id}`)
}
}
]
module.exports = mockResponses
The individual resource module:
const users = require('./users.json')
/* responses for /users/:id */
const mockResponses = [
/* don't support POST here */
{ request: { method: 'POST' }, response: { status: 400 } },
/* for GET requests, return a particular user */
{
request: { method: 'GET' },
response: function (ctx, id) {
ctx.body = users.find(user => user.id === Number(id))
}
},
/* for PUT requests, update the record */
{
request: { method: 'PUT' },
response: function (ctx, id) {
const updatedUser = ctx.request.body
const existingUserIndex = users.findIndex(user => user.id === Number(id))
users.splice(existingUserIndex, 1, updatedUser)
ctx.status = 200
}
},
/* DELETE request: remove the record */
{
request: { method: 'DELETE' },
response: function (ctx, id) {
const existingUserIndex = users.findIndex(user => user.id === Number(id))
users.splice(existingUserIndex, 1)
ctx.status = 200
}
}
]
module.exports = mockResponses