test: track callback invocations

Use `common.mustCall()` and `common.mustNotCall()` to check that
callbacks are invoked the expected number of times in
test-net-listen-shared-ports.

PR-URL: https://github.com/nodejs/node/pull/13010
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

test/sequential/test-net-listen-shared-ports.js

@@ -4,24 +4,22 @@ const assert = require('assert');
 const cluster = require('cluster');
 const net = require('net');
 
-function noop() {}
-
 if (cluster.isMaster) {
   const worker1 = cluster.fork();
 
-  worker1.on('message', function(msg) {
+  worker1.on('message', common.mustCall(function(msg) {
     assert.strictEqual(msg, 'success');
     const worker2 = cluster.fork();
 
-    worker2.on('message', function(msg) {
+    worker2.on('message', common.mustCall(function(msg) {
       assert.strictEqual(msg, 'server2:EADDRINUSE');
       worker1.kill();
       worker2.kill();
-    });
-  });
+    }));
+  }));
 } else {
-  const server1 = net.createServer(noop);
-  const server2 = net.createServer(noop);
+  const server1 = net.createServer(common.mustNotCall());
+  const server2 = net.createServer(common.mustNotCall());
 
   server1.on('error', function(err) {
     // no errors expected
@@ -37,10 +35,12 @@ if (cluster.isMaster) {
     host: 'localhost',
     port: common.PORT,
     exclusive: false
-  }, function() {
-    server2.listen({port: common.PORT + 1, exclusive: true}, function() {
+  }, common.mustCall(function() {
+    server2.listen({port: common.PORT + 1, exclusive: true},
+                   common.mustCall(function() {
                      // the first worker should succeed
                      process.send('success');
-    });
-  });
+                   })
+    );
+  }));
 }