feature: improve server start error message (#256)

packages/preview-process/src/parts/WebViewServerState/WebViewServerState.ts

@@ -1,13 +1,17 @@
 import type { WebViewServer } from '../WebViewServerTypes/WebViewServerTypes.ts'
 
-const servers = Object.create(null)
+const servers: Record<number, WebViewServer> = Object.create(null)
 
 export const set = (id: number, server: WebViewServer): void => {
   servers[id] = server
 }
 
 export const get = (id: number): WebViewServer => {
-  return servers[id]
+  const server = servers[id]
+  if (!server) {
+    throw new Error(`Server with id ${id} not found`)
+  }
+  return server
 }
 
 export const has = (id: number): boolean => {

packages/test-integration/test/PreviewProcessStartWithoutCreate.test.ts

@@ -8,7 +8,7 @@ test('preview process - handles port already in use', async () => {
   const port = await getPort()
   // TODO improve error message
   await expect(previewProcess1.invoke('WebViewServer.start', id, port)).rejects.toThrow(
-    "Failed to start webview server: TypeError: Cannot read properties of undefined (reading 'server')",
+    'Failed to start webview server: Server with id 1 not found',
   )
   previewProcess1[Symbol.dispose]()
 })