Update README for new test helper.

README.md

@@ -143,12 +143,40 @@ SignedForm.config do |c|
   c.digest_store = SignedForm::DigestStores::NullStore.new
   c.secret_key   = 'supersecret'
 end
-
 ```
 
 Those options that are in the options hash are the default per-form options. They can be overridden by passing the same
 option to the `signed_form_for` method.
 
+## Testing Your Controllers
+
+Because your tests won't include a signature you will get a `ForbiddenAttributes` exception in your tests that do mass
+assignment. SignedForm includes a helper that works with both TestUnit and RSpec to help.
+
+Since you're using SignedForm there is no need test attribute assignment so you may as well permit all attributes. Which
+is the name of the helper SignedForm provides. In your `spec_helper` file or `test_helper` file `require
+'signed_form/test_helper'`. Once you do this `permit_all_attributes` is available in your tests/specs.
+
+**Caution** `permit_all_attributes` modifies the class of the controller instance under test for the duration of the
+test. If you want to restore the class mid-test `permit_all_attributes` takes an optional block. Example:
+
+```ruby
+  describe "POST create" do
+    describe "with valid params" do
+      it "assigns a newly created car as @car" do
+        permit_all_parameters do
+          post :create, {:car => valid_attributes}, valid_session
+          assigns(:car).should be_a(Car)
+          assigns(:car).should be_persisted
+        end
+        assigns(:car).should be_nil # This is nil because it was never set on the original controller
+      end
+    end
+  end
+```
+
+But this block shouldn't normally be needed. Again the controller class is only affected for the current test.
+
 ## I want to hear from you
 
 If you're using SignedForm, I'd love to hear from you. What do you like? What could be better? I'd love to hear your