def user_exists?(username)
      begin
        url = url_for_path(user_path(username))
        client.get(url) { |response| response.code == 200 }
      rescue
        raise 'Error: Could not test user existence!'
      end
    end
def user_exists?(username)
      begin
        url = url_for_path(user_path(username))
        client.get(url) { |response| response.code == 200 }
      rescue
        raise 'Error: Could not test user existence!'
      end
    end
Tests if the user given its username exists..

 @param username
 @return [Boolean]

 ====Examples
 @example
   @coach.user_exsists?('arueedlinger')