add test for when expires fails because of Time.parse

Signed-off-by: Konstantin Haase <konstantin.mailinglists@googlemail.com>

test/helpers_test.rb

@@ -646,6 +646,10 @@ class HelpersTest < Test::Unit::TestCase
           expires obj, :public, :no_cache
           'Hello World'
         end
+
+        get '/boom' do
+          expires '1000'
+        end
       end
     end
 
@@ -673,6 +677,10 @@ class HelpersTest < Test::Unit::TestCase
       get '/blah'
       assert_equal ['public', 'no-cache', 'max-age=60'], response['Cache-Control'].split(', ')
     end
+
+    it 'fails when Time.parse raises an ArgumentError' do
+      assert_raise(RuntimeError) { get '/boom' }
+    end
   end
 
   describe 'last_modified' do