add test to confirm coffee errors show correctly

features/coffee-script.feature

@@ -9,4 +9,9 @@ Feature: Support coffee-script
   Scenario: Rendering coffee-script with :coffeescript haml-filter
     Given the Server is running
     When I go to "/inline-coffeescript.html"
-    Then I should see "Array.prototype.slice"
+    Then I should see "Array.prototype.slice"
+  
+  Scenario: Rendering broken coffee
+    Given the Server is running
+    When I go to "/javascripts/broken-coffee.js"
+    Then I should see "Reserved word"

fixtures/test-app/source/javascripts/broken-coffee.js.coffee

@@ -0,0 +1,3 @@
+function test() {
+  hello
+}