test: test cluster worker disconnection on error

This test checks that ownerless cluster worker handles are closed
correctly on disconnection.

Fixes: https://github.com/nodejs/node/issues/6561
PR-URL: https://github.com/nodejs/node/pull/6909
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-cluster-worker-disconnect-on-error.js

@@ -0,0 +1,20 @@
+'use strict';
+const common = require('../common');
+const http = require('http');
+const cluster = require('cluster');
+
+cluster.schedulingPolicy = cluster.SCHED_NONE;
+
+const server = http.createServer();
+if (cluster.isMaster) {
+  server.listen(common.PORT);
+  const worker = cluster.fork();
+  worker.on('exit', common.mustCall(() => {
+    server.close();
+  }));
+} else {
+  server.listen(common.PORT);
+  server.on('error', common.mustCall((e) => {
+    cluster.worker.disconnect();
+  }));
+}