test: add tests to check error in dns.lookupService.

Added tests to check error in dns.lookupService to
increase coverage.

PR-URL: #22908
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Weijia Wang <[email protected]>
Reviewed-By: Sakthipriyan Vairamani <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: Masashi Hirano

test/parallel/test-dns-lookupService.js

@@ -0,0 +1,20 @@
+// Flags: --expose-internals
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { internalBinding } = require('internal/test/binding');
+const cares = internalBinding('cares_wrap');
+const { UV_ENOENT } = internalBinding('uv');
+const dns = require('dns');
+
+// Stub `getnameinfo` to *always* error.
+cares.getnameinfo = () => UV_ENOENT;
+
+assert.throws(
+  () => dns.lookupService('127.0.0.1', 80, common.mustNotCall()),
+  {
+    code: 'ENOENT',
+    message: 'getnameinfo ENOENT 127.0.0.1',
+    syscall: 'getnameinfo'
+  }
+);