test: add coverage to dgram receive error case

This commit adds coverage for the case where a dgram socket
handle receives a message, but nread < 0, indicating an error.

PR-URL: nodejs#11241
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>

test/parallel/test-dgram-recv-error.js

@@ -0,0 +1,16 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const dgram = require('dgram');
+const s = dgram.createSocket('udp4');
+
+s.on('error', common.mustCall((err) => {
+  s.close();
+
+  // Don't check the full error message, as the errno is not important here.
+  assert(/^Error: recvmsg/.test(err));
+  assert.strictEqual(err.syscall, 'recvmsg');
+}));
+
+s.on('message', common.mustNotCall('no message should be received.'));
+s.bind(common.mustCall(() => s._handle.onmessage(-1, s._handle, null, null)));