Add stub for ApplicationHelper spec.
user
```ruby
require 'spec_helper'

# Specs in this file have access to a helper object that includes
# the ChallengesHelper. For example:
#
# describe ChallengesHelper do
#   describe "string concat" do
#     it "concats two strings with spaces" do
#       expect(helper.concat_strings("this","that")).to eq("this that")
#     end
#   end
# end
describe ApplicationHelper do
  describe 'within_team_registration_period?' do
  end

  describe 'within_contest_period?' do
  end

  describe 'markdown_render' do
  end
end
```
assistant