Adding simple working validating test

package.json

@@ -38,6 +38,7 @@
     "elysia": ">= 0.7.0"
   },
   "devDependencies": {
+    "@apidevtools/swagger-parser": "^10.1.0",
     "@types/node": "^20.1.4",
     "bun-types": "^0.7.0",
     "elysia": "0.7.10",

test/index.test.ts

@@ -1,7 +1,9 @@
 import { Elysia, t } from 'elysia'
+import SwaggerParser from '@apidevtools/swagger-parser';
 import { swagger } from '../src'
 
 import { describe, expect, it } from 'bun:test'
+import { fail } from 'assert';
 
 const req = (path: string) => new Request(`http://localhost${path}`)
 
@@ -13,6 +15,13 @@ describe('Swagger', () => {
         expect(res.status).toBe(200)
     })
 
+    it('returns a valid Swagger/OpenAPI json config', async () => {
+        const app = new Elysia().use(swagger())
+        const res = await app.handle(req('/swagger/json')).then((x) => x.json());
+        expect(res.openapi).toBe("3.0.3");
+        await SwaggerParser.validate(res).catch((err) => fail(err));
+    });
+
     it('use custom Swagger version', async () => {
         const app = new Elysia().use(
             swagger({