Data science up for first round of review

1) Focus on rspec tests 
2) Stuck at trying to refactor the exception part
avoid using '@' symbol outside of init statements. since group_one and group_two are class variables, and defined by accessors, calling `group_one` anywhere in the scope of the class automagically calls `self.group_one`, also clears up your class so that the attribute is only ever set in one place (init preferably), otherwise you may find yourself replacing @variable_name over and over in your code if it's value is changed or mutated outside of class scope. Example:
<pre>
class TestClass
   attr_accessor :name, :total, :etc
   def initialize(name, total, etc)
     @name ||= name || 'none'
     @total ||= total || 0
     @etc ||= etc || 'blah'
     end
   def to_s
     "#{name} #{total} #{etc}"
     end
   end
<pre>