test: test prefix behavior documented in doc

README.md

@@ -339,6 +339,15 @@ Each plugin can be individually configured using the following module properties
   }
   ```
 
+  However, note that the `prefix` option should be set directly on `autoConfig` for autoloading to work as expected:
+  ```js
+  export const autoConfig = (fastify) => {
+    return { name: 'y ' + fastify.rootName }
+  }
+
+  autoConfig.prefix = '/hello'
+  ```
+
 - `plugin.autoPrefix` - Set routing prefix for plugin
 
   ```js

test/commonjs/basic.js

@@ -3,7 +3,7 @@
 const t = require('tap')
 const Fastify = require('fastify')
 
-t.plan(101)
+t.plan(107)
 
 const app = Fastify()
 
@@ -270,4 +270,22 @@ app.ready(function (err) {
     t.equal(res.statusCode, 200)
     t.same(JSON.parse(res.payload), { works: true })
   })
+
+  app.inject({
+    url: '/configPrefix'
+  }, function (err, res) {
+    t.error(err)
+
+    t.equal(res.statusCode, 200)
+    t.same(JSON.parse(res.payload), { configPrefix: true })
+  })
+
+  app.inject({
+    url: '/configPrefixCallback'
+  }, function (err, res) {
+    t.error(err)
+
+    t.equal(res.statusCode, 200)
+    t.same(JSON.parse(res.payload), { configPrefixCallback: true })
+  })
 })

test/commonjs/basic/foo/configPrefix.js

@@ -0,0 +1,13 @@
+'use strict'
+
+module.exports = function (f, opts, next) {
+  f.get('/', (request, reply) => {
+    reply.send({ configPrefix: true })
+  })
+
+  next()
+}
+
+module.exports.autoConfig = {
+  prefix: '/configPrefix'
+}

test/commonjs/basic/foo/configPrefixCallback.js

@@ -0,0 +1,14 @@
+'use strict'
+
+module.exports = function (f, opts, next) {
+  f.get('/', (request, reply) => {
+    reply.send({ configPrefixCallback: true })
+  })
+
+  next()
+}
+
+const options = () => ({})
+options.prefix = '/configPrefixCallback'
+
+module.exports.autoConfig = options

test/module/basic.js

@@ -2,7 +2,7 @@ import t from 'tap'
 import fastify from 'fastify'
 import basicApp from './basic/app.js'
 
-t.plan(74)
+t.plan(80)
 
 const app = fastify()
 
@@ -227,4 +227,22 @@ app.ready(function (err) {
       statusCode: 404
     })
   })
+
+  app.inject({
+    url: '/configPrefix'
+  }, function (err, res) {
+    t.error(err)
+
+    t.equal(res.statusCode, 200)
+    t.same(JSON.parse(res.payload), { configPrefix: true })
+  })
+
+  app.inject({
+    url: '/configPrefixCallback'
+  }, function (err, res) {
+    t.error(err)
+
+    t.equal(res.statusCode, 200)
+    t.same(JSON.parse(res.payload), { configPrefixCallback: true })
+  })
 })

test/module/basic/foo/configPrefix.js

@@ -0,0 +1,13 @@
+'use strict'
+
+export default function (f, opts, next) {
+  f.get('/', (request, reply) => {
+    reply.send({ configPrefix: true })
+  })
+
+  next()
+}
+
+export const autoConfig = {
+  prefix: '/configPrefix'
+}

test/module/basic/foo/configPrefixCallback.js

@@ -0,0 +1,12 @@
+'use strict'
+
+export default function (f, opts, next) {
+  f.get('/', (request, reply) => {
+    reply.send({ configPrefixCallback: true })
+  })
+
+  next()
+}
+
+export const autoConfig = () => ({})
+autoConfig.prefix = '/configPrefixCallback'