test: add test suite for onPlugIn event handler

cheetah.ts

@@ -244,7 +244,7 @@ export class cheetah extends base<cheetah>() {
       let body: Response | void = undefined
 
       for (const e of this.#extensions.values()) {
-        if (this.#onPlugIn === true && e[1].onPlugIn !== undefined) {
+        if (!this.#onPlugIn && e[1].onPlugIn !== undefined) {
           await e[1].onPlugIn({
             env: __app.env,
             routes: this.#routes,
@@ -290,8 +290,8 @@ export class cheetah extends base<cheetah>() {
         }
       }
 
-      if (this.#onPlugIn) {
-        this.#onPlugIn = false
+      if (!this.#onPlugIn) {
+        this.#onPlugIn = true
       }
 
       if (body !== undefined) {

test/extensions.test.ts

@@ -3,7 +3,14 @@ import cheetah, { createExtension } from '../mod.ts'
 import { assertEquals } from './deps.ts'
 
 Deno.test('Extensions', async (t) => {
+  let count = 0
+
   const a = createExtension({
+    onPlugIn({ setRoute }) {
+      setRoute('get', '/cookie', () => '🍪')
+
+      count++
+    },
     onRequest({ req }) {
       req.headers.set('custom', 'test')
     },
@@ -39,6 +46,12 @@ Deno.test('Extensions', async (t) => {
       return 'test'
     })
 
+  await t.step('onPlugIn (part 1)', async () => {
+    const result = await app.fetch(new Request('http://localhost/cookie'))
+
+    assertEquals(await result.text(), '🍪')
+  })
+
   await t.step('onRequest', async () => {
     const result = await app.fetch(new Request('http://localhost/a'))
 
@@ -54,4 +67,11 @@ Deno.test('Extensions', async (t) => {
 
     assertEquals(await result2.text(), 'hello')
   })
+
+  await t.step('onPlugIn (part 2)', async () => {
+    const result = await app.fetch(new Request('http://localhost/cookie'))
+
+    assertEquals(await result.text(), '🍪')
+    assertEquals(count, 1)
+  })
 })