gistfile1.rb

2.0.0p0 :001 > x = ActionController::Parameters.new(a: {b: "foo"})
 => {"a"=>{"b"=>"foo"}} 
2.0.0p0 :002 > x.require(:a).permit(:b)
 => {"b"=>"foo"} 
2.0.0p0 :003 > include ActionDispatch::TestProcess
 => Object 
2.0.0p0 :004 > x = ActionController::Parameters.new(a: {b: fixture_file_upload("spec/test.jpg")})
 => {"a"=>{"b"=>#<Rack::Test::UploadedFile:0x007ffaa5cb8b88 @content_type=nil, @original_filename="test.jpg", @tempfile=#<Tempfile:/var/folders/pb/3546xrb11pl1cl34gdx9jrsc0000gn/T/test.jpg20130511-7104-1w3q5j9>>}} 
2.0.0p0 :005 > x.require(:a).permit(:b)
ActionController::UnpermittedParameters: found unpermitted parameters: b
  from /Users/ejp/.rvm/gems/ruby-2.0.0-p0@ufc-tracker/gems/strong_parameters-0.2.0/lib/action_controller/parameters.rb:221:in `unpermitted_parameters!'
	from /Users/ejp/.rvm/gems/ruby-2.0.0-p0@ufc-tracker/gems/strong_parameters-0.2.0/lib/action_controller/parameters.rb:72:in `permit'
	from (irb):5
	from /Users/ejp/.rvm/gems/ruby-2.0.0-p0@ufc-tracker/gems/railties-3.2.13/lib/rails/commands/console.rb:47:in `start'
	from /Users/ejp/.rvm/gems/ruby-2.0.0-p0@ufc-tracker/gems/railties-3.2.13/lib/rails/commands/console.rb:8:in `start'
	from /Users/ejp/.rvm/gems/ruby-2.0.0-p0@ufc-tracker/gems/railties-3.2.13/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'