test: make test-tls-alert-handling more strict

Use `common.mustCall()` and `common.mustNotCall()` to more rigorously
check that functions (especially no-op error handlers) are called the
expected number of times in test-tls-alert-handling.

PR-URL: #14650
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: David Cai <davidcai1993@yahoo.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

test/parallel/test-tls-alert-handling.js

@@ -5,33 +5,43 @@ if (!common.hasCrypto)
   common.skip('missing crypto');
 
 if (!common.opensslCli)
-  common.skip('node compiled without OpenSSL CLI.');
+  common.skip('node compiled without OpenSSL CLI');
 
 const net = require('net');
 const tls = require('tls');
 const fixtures = require('../common/fixtures');
 
+let clientClosed = false;
+let errorReceived = false;
+function canCloseServer() {
+  return clientClosed && errorReceived;
+}
+
 function loadPEM(n) {
-  return fixtures.readKey(`${n}.pem`);
+  return fixtures.readKey(`${n}.pem`, 'utf-8');
 }
 
 const opts = {
   key: loadPEM('agent2-key'),
   cert: loadPEM('agent2-cert')
 };
+
 const max_iter = 20;
 let iter = 0;
 
-const server = tls.createServer(opts, function(s) {
-  s.pipe(s);
-  s.on('error', function() {
-    // ignore error
-  });
+const errorHandler = common.mustCall(() => {
+  errorReceived = true;
+  if (canCloseServer())
+    server.close();
 });
+const server = tls.createServer(opts, common.mustCall(function(s) {
+  s.pipe(s);
+  s.on('error', errorHandler);
+}, 2));
 
-server.listen(0, function() {
+server.listen(0, common.mustCall(function() {
   sendClient();
-});
+}));
 
 
 function sendClient() {
@@ -45,15 +55,14 @@ function sendClient() {
       return;
     }
     client.end();
-    server.close();
   }, max_iter));
   client.write('a');
-  client.on('error', function() {
-    // ignore error
-  });
-  client.on('close', function() {
-    server.close();
-  });
+  client.on('error', common.mustNotCall());
+  client.on('close', common.mustCall(function() {
+    clientClosed = true;
+    if (canCloseServer())
+      server.close();
+  }));
 }
 
 
@@ -63,11 +72,9 @@ function sendBADTLSRecord() {
   const client = tls.connect({
     socket: socket,
     rejectUnauthorized: false
-  }, function() {
+  }, common.mustCall(function() {
     socket.write(BAD_RECORD);
     socket.end();
-  });
-  client.on('error', function() {
-    // ignore error
-  });
+  }));
+  client.on('error', common.mustCall());
 }