feat: preserve undici agent by default

Documentation states destroyAgent defaults to false but
the option was undefined when omitted, causing custom ag
ents to be destroyed. Explicitly default the option to f
alse and cover it with a regression test.

Signed-off-by: Yukio Ueda <triangle.pillow@gmail.com>

Author: Yukio0315

lib/request.js

@@ -53,7 +53,7 @@ function buildRequest (opts) {
   const isBalanced = Array.isArray(opts.base) && opts.base.length > 1
   const undiciOpts = opts.undici || {}
   const globalAgent = opts.globalAgent
-  const destroyAgent = opts.destroyAgent
+  const destroyAgent = opts.destroyAgent || false
   let http2Client
   let undiciAgent
   let undiciInstance

test/undici-no-destroy.test.js

@@ -27,3 +27,25 @@ test('destroyAgent false', async (t) => {
   await instance.ready()
   await instance.close()
 })
+
+test('destroyAgent default false', async (t) => {
+  const mockAgent = new undici.Agent()
+  mockAgent.destroy = () => {
+    t.fail()
+  }
+  const instance = Fastify()
+
+  t.after(() => instance.close())
+
+  instance.get('/', (_request, reply) => {
+    reply.from()
+  })
+
+  instance.register(From, {
+    base: 'http://localhost:4242',
+    undici: mockAgent
+  })
+
+  await instance.ready()
+  await instance.close()
+})