fix: properly shut down server

src/launcher.ts

@@ -1,10 +1,9 @@
 import path from 'node:path'
 import url from 'node:url'
-import cp from 'node:child_process'
+import cp, { type ChildProcess } from 'node:child_process'
 
 import logger from '@wdio/logger'
 import getPort from 'get-port'
-import type { NextServer } from 'next/dist/server/next.js'
 
 import { pkg } from './constants.js'
 import { lookupNextConfig } from './utils.js'
@@ -14,7 +13,7 @@ const log = logger('wdio-next-service')
 
 export class NuxtServiceLauncher {
     #options: Required<NextServiceOptions>
-    #server?: NextServer
+    #server?: ChildProcess
 
     constructor (options: NextServiceOptions) {
         log.info(`Initiate Next Service (v${pkg.version})`)
@@ -43,49 +42,50 @@ export class NuxtServiceLauncher {
 
         log.info(`Start Next.js dev server on ${this.#options.hostname}:${port}`)
         const startServerPath = import.meta.resolve('next/dist/server/lib/start-server.js')
-        const child = cp.fork(url.fileURLToPath(startServerPath), {
-            stdio: 'inherit',
-            cwd: path.dirname(nextjsConfigPath),
-            env: {
-                ...process.env,
-                WDIO_NEXT_SERVICE: '1',
-                NEXT_PRIVATE_WORKER: '1'
-            }
-        })
-
         await new Promise<void>((resolve) => {
             let resolved = false
+            this.#server = cp.fork(url.fileURLToPath(startServerPath), {
+                stdio: 'inherit',
+                cwd: path.dirname(nextjsConfigPath),
+                env: {
+                    ...process.env,
+                    WDIO_NEXT_SERVICE: '1',
+                    NEXT_PRIVATE_WORKER: '1'
+                }
+            })
+
             const nextWorkerOptions = {
                 port,
                 dir: path.dirname(nextjsConfigPath),
                 allowRetry: true,
                 isDev
             }
-            child.on('message', (msg: any) => {
+
+            this.#server.on('message', (msg: any) => {
                 if (msg && typeof msg === 'object') {
-                    if (msg.nextWorkerReady) {
-                        child.send({ nextWorkerOptions })
+                    if (msg.nextWorkerReady && this.#server) {
+                        this.#server.send({ nextWorkerOptions })
                     } else if (msg.nextServerReady && !resolved) {
                         resolved = true
                         resolve()
                     }
                 }
             })
-            child.on('error', (err) => {
+            this.#server.on('error', (err) => {
                 log.error('Failed to start Next.js server', err)
             })
-            child.on('exit', (code, signal) => {
+            this.#server.on('exit', (code, signal) => {
                 log.info(`Next.js dev server stopped with exit code ${code} and signal ${signal}`)
             })
         })
 
         process.env.WDIO_BASE_URL = `http://${this.#options.hostname}:${port}`
     }
 
-    public async onComplete () {
-        log.info('Stop Next.js dev server')
+    public onComplete () {
         if (this.#server) {
-            await this.#server.close()
+            log.info('Stop Next.js dev server')
+            this.#server.kill()
         }
     }
 }