test: added net.connect lookup type check

Check the options passed to Socket.prototype.connect() to
validate the type of the lookup property.

PR-URL: https://github.com/nodejs/node/pull/11873
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

test/parallel/test-net-options-lookup.js

@@ -0,0 +1,34 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+const expectedError = /^TypeError: "lookup" option should be a function$/;
+
+['foobar', 1, {}, []].forEach((input) => connectThrows(input));
+
+function connectThrows(input) {
+  const opts = {
+    host: 'localhost',
+    port: common.PORT,
+    lookup: input
+  };
+
+  assert.throws(function() {
+    net.connect(opts);
+  }, expectedError);
+}
+
+[() => {}].forEach((input) => connectDoesNotThrow(input));
+
+function connectDoesNotThrow(input) {
+  const opts = {
+    host: 'localhost',
+    port: common.PORT,
+    lookup: input
+  };
+
+  assert.doesNotThrow(function() {
+    net.connect(opts);
+  });
+}