diff --git a/src/net/hook.go b/src/net/hook.go
new file mode 100644
index 0000000..14dc19f
--- /dev/null
+++ b/src/net/hook.go
@@ -0,0 +1,7 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package net
+
+var testHookLookupIP = func(fn func(string) ([]IPAddr, error), host string) ([]IPAddr, error) { return fn(host) }