chore(ipv6): only run ipv6 e2e test in ipv6 environment

test/e2e/ipv6.spec.ts

@@ -3,9 +3,9 @@ import { getLocal } from 'mockttp';
 import request from 'supertest';
 import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 
-import { createApp, createProxyMiddleware } from './test-kit.js';
+import { createApp, createProxyMiddleware, isIPv6Available } from './test-kit.js';
 
-describe('ipv6 integration', () => {
+describe.runIf(await isIPv6Available())('ipv6 integration', () => {
   let targetServer: Mockttp;
 
   beforeEach(async () => {

test/e2e/test-kit.ts

@@ -1,3 +1,5 @@
+import { createServer } from 'node:net';
+
 import express, { type Express, type RequestHandler } from 'express';
 
 export {
@@ -18,3 +20,21 @@ export function createAppWithPath(path: string | string[], middleware: RequestHa
   app.use(path, middleware);
   return app;
 }
+
+/**
+ * Detects if the current environment supports IPv6
+ * Used to conditionally run tests that require IPv6 support
+ */
+export async function isIPv6Available(): Promise<boolean> {
+  return new Promise((resolve) => {
+    const server = createServer();
+
+    const done = (result: boolean) => {
+      server.removeAllListeners('error');
+      server.close(() => resolve(result));
+    };
+
+    server.once('error', () => done(false));
+    server.listen(0, '::1', () => done(true));
+  });
+}