test: dns existence from resource url

deno.json

@@ -3,7 +3,8 @@
     "config:generate": "deno run --allow-net --allow-write ./src/config/generate.ts",
     "build": "deno run -R -W ./src/build.js",
     "lint": "deno fmt --check ./src ./test",
-    "tests": "deno test --allow-read"
+    "tests": "deno test --allow-read --allow-env",
+    "tests:dns": "VALIDATE_DNS=1 deno test --allow-read --allow-env --allow-net"
   },
   "imports": {
     "@std/path": "jsr:@std/path@^1.0.8",

test/filters.test.ts

@@ -3,10 +3,25 @@ import { expect } from "jsr:@std/expect";
 import { readFileSync } from "node:fs";
 import path from "node:path";
 import process from "node:process";
+import dns from "node:dns/promises";
+import * as tldts from "npm:tldts";
 import { parse } from "../src/assert.ts";
 
+const VALIDATE_DNS = !!Deno.env.get("VALIDATE_DNS");
 const cwd = process.cwd();
 
+const hasDnsRecord = async (hostname: string) => {
+  for (const rr of ["A", "AAAA", "CNAME"]) {
+    if (
+      await dns.resolve(hostname, rr)
+        .catch((_error) => false as const)
+    ) {
+      return;
+    }
+  }
+  throw new Error("RECORD_NOT_FOUND: " + hostname);
+};
+
 const doTest = (filePath: string) => {
   const content = readFileSync(path.join(cwd, filePath), "utf8");
 
@@ -18,7 +33,7 @@ const doTest = (filePath: string) => {
       continue;
     }
 
-    Deno.test(filter, () => {
+    Deno.test(filter, async () => {
       const parsed = parseFilter(filter);
 
       // Is a valid filter
@@ -37,6 +52,11 @@ const doTest = (filePath: string) => {
         expect((NetworkFilter.parse(filter)!).match(
           Request.fromRawDetails({ url, type, sourceUrl: source }),
         )).toBe(match);
+
+        if (VALIDATE_DNS && url) {
+          await expect(hasDnsRecord(tldts.parse(url)!.hostname!))
+            .resolves.not.toThrow();
+        }
       }
     });
   }