test: add comments explaining _setSimultaneousAccepts deprecation tests

PR-URL: nodejs#41307
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

test/parallel/test-net-deprecated-setsimultaneousaccepts.js

@@ -1,6 +1,8 @@
 // Flags: --no-warnings
 'use strict';
 
+// Test that DEP0121 is emitted on the first call of _setSimultaneousAccepts().
+
 const {
   expectWarning
 } = require('../common');

test/parallel/test-net-server-simultaneous-accepts-produce-warning-once.js

@@ -1,12 +1,19 @@
 'use strict';
 
+// Test that DEP0121 is emitted only once if _setSimultaneousAccepts() is called
+// more than once. This test is similar to
+// test-net-deprecated-setsimultaneousaccepts.js, but that test calls
+// _setSimultaneousAccepts() only once. Unlike this test, that will confirm
+// that the warning is emitted on the first call. This test doesn't check which
+// call caused the warning to be emitted.
+
 const { expectWarning } = require('../common');
-const net = require('net');
+const { _setSimultaneousAccepts } = require('net');
 
 expectWarning(
   'DeprecationWarning',
   'net._setSimultaneousAccepts() is deprecated and will be removed.',
   'DEP0121');
 
-net._setSimultaneousAccepts();
-net._setSimultaneousAccepts();
+_setSimultaneousAccepts();
+_setSimultaneousAccepts();