test: test net.connect monkey patching

This is important for people who monkey-patches
`Socket.prototype.connect` since it's not possible to monkey-patch
`net.connect` directly (as the core `connect` function is called
internally in Node instead of calling the `exports.connect` function).

Monkey-patching of `Socket.prototype.connect` is done by - among others
- most APM vendors, the async-listener module and the
continuation-local-storage module.

test/parallel/test-net-connect-call-socket-connect.js

@@ -0,0 +1,37 @@
+'use strict';
+
+// This test checks that calling `net.connect` internally calls
+// `Socket.prototype.connect`.
+//
+// This is important for people who monkey-patch `Socket.prototype.connect`
+// since it's not possible to monkey-patch `net.connect` directly (as the core
+// `connect` function is called internally in Node instead of calling the
+// `exports.connect` function).
+//
+// Monkey-patching of `Socket.prototype.connect` is done by - among others -
+// most APM vendors, the async-listener module and the
+// continuation-local-storage module.
+//
+// See https://github.com/nodejs/node/pull/12852 for details.
+
+const common = require('../common');
+const net = require('net');
+const Socket = net.Socket;
+
+// monkey patch Socket.prototype.connect to check that it's called
+const orig = Socket.prototype.connect;
+Socket.prototype.connect = common.mustCall(function() {
+  return orig.apply(this, arguments);
+});
+
+const server = net.createServer();
+
+server.listen(common.mustCall(function() {
+  const port = server.address().port;
+  const client = net.connect({port}, common.mustCall(function() {
+    client.end();
+  }));
+  client.on('end', common.mustCall(function() {
+    server.close();
+  }));
+}));