rackspace preview stack op and unit test
diff --git a/rackspace/orchestration/v1/stacks/delegate_test.go b/rackspace/orchestration/v1/stacks/delegate_test.go
index 452a5ba..eb4e171 100644
--- a/rackspace/orchestration/v1/stacks/delegate_test.go
+++ b/rackspace/orchestration/v1/stacks/delegate_test.go
@@ -398,3 +398,47 @@
 	err := Delete(fake.ServiceClient(), "gophercloud-test-stack-2", "db6977b2-27aa-4775-9ae7-6213212d4ada").ExtractErr()
 	th.AssertNoErr(t, err)
 }
+
+func TestPreviewStack(t *testing.T) {
+	th.SetupHTTP()
+	defer th.TeardownHTTP()
+	os.HandlePreviewSuccessfully(t, os.GetOutput)
+
+	previewOpts := os.PreviewOpts{
+		Name:    "stackcreated",
+		Timeout: 60,
+		Template: `
+    {
+      "stack_name": "postman_stack",
+      "template": {
+        "heat_template_version": "2013-05-23",
+        "description": "Simple template to test heat commands",
+        "parameters": {
+          "flavor": {
+            "default": "m1.tiny",
+            "type": "string"
+          }
+        },
+        "resources": {
+          "hello_world": {
+            "type":"OS::Nova::Server",
+            "properties": {
+              "key_name": "heat_key",
+              "flavor": {
+                "get_param": "flavor"
+              },
+              "image": "ad091b52-742f-469e-8f3c-fd81cadf0743",
+              "user_data": "#!/bin/bash -xv\necho \"hello world\" > /root/hello-world.txt\n"
+            }
+          }
+        }
+      }
+    }`,
+		DisableRollback: os.Disable,
+	}
+	actual, err := Preview(fake.ServiceClient(), previewOpts).Extract()
+	th.AssertNoErr(t, err)
+
+	expected := os.PreviewExpected
+	th.AssertDeepEquals(t, expected, actual)
+}