Don't allow customers to be updated with failing credit cards.

lib/fake_braintree/customer.rb

@@ -24,9 +24,13 @@ def create
 
     def update
       if customer_exists_in_registry?
-        updates = customer_hash
-        updated_customer = update_existing_customer(updates)
-        response_for_updated_customer(updated_customer)
+        if credit_card_is_failure?
+          response_for_invalid_card
+        else
+          updates = customer_hash
+          updated_customer = update_existing_customer(updates)
+          response_for_updated_customer(updated_customer)
+        end
       else
         response_for_customer_not_found
       end

spec/fake_braintree/customer_spec.rb

@@ -109,6 +109,15 @@
   it "raises an error for a nonexistent customer" do
     lambda { Braintree::Customer.update("foo", {:first_name => "Bob"}) }.should raise_error(Braintree::NotFoundError)
   end
+
+  it "does not allow a customer to be updated to a failing credit card" do
+    bad_credit_card = "123456"
+    FakeBraintree.registry.failures[bad_credit_card] = FakeBraintree.failure_response
+
+    customer = create_customer
+    result =  Braintree::Customer.update(customer.customer.id, {:credit_card => { :number => bad_credit_card }})
+    result.should_not be_success
+  end
 end
 
 describe "Braintree::Customer.delete" do