test: minor refactoring

Add punctuation and comments about code that should not throw.
Also remove a obsolete test and refactor some tests.

Backport-PR-URL: #19244
PR-URL: #18669
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: BridgeAR

test/addons/symlinked-module/test.js

@@ -30,5 +30,5 @@ const sub = require('./submodule');
   const mod = require(path.join(i, 'binding.node'));
   assert.notStrictEqual(mod, null);
   assert.strictEqual(mod.hello(), 'world');
-  sub.test(i);
+  sub.test(i); // Should not throw.
 });

test/internet/test-dns.js

@@ -579,11 +579,8 @@ process.on('exit', function() {
   assert.ok(getaddrinfoCallbackCalled);
 });
 
-
+// Should not throw.
 dns.lookup(addresses.INET6_HOST, 6, common.mustCall());
-
 dns.lookup(addresses.INET_HOST, {}, common.mustCall());
-
 dns.lookupService('0.0.0.0', '0', common.mustCall());
-
 dns.lookupService('0.0.0.0', 0, common.mustCall());