test: add check in test-signal-handler

* Check that the removed listener is not called.
* Opportunistic `==` -> `===` change.

PR-URL: #8248
Reviewed-By: Colin Ihrig <[email protected]>

Author: Trott

test/parallel/test-signal-handler.js

@@ -22,14 +22,14 @@ var i = 0;
 setInterval(function() {
   console.log('running process...' + ++i);
 
-  if (i == 5) {
+  if (i === 5) {
     process.kill(process.pid, 'SIGUSR1');
   }
 }, 1);
 
 // Test on condition where a watcher for SIGNAL
 // has been previously registered, and `process.listeners(SIGNAL).length === 1`
-process.on('SIGHUP', function() {});
+process.on('SIGHUP', function() { common.fail('should not run'); });
 process.removeAllListeners('SIGHUP');
 process.on('SIGHUP', common.mustCall(function() {}));
 process.kill(process.pid, 'SIGHUP');