dna.rb

class DNATest < MiniTest::Unit::TestCase

  # You don't have to put your classes inside of the test case, but it
  # doesn't hurt for these examples
  class DNA
    def initialize(string)
      @string = string
      # You can provide a default value for hashes. This also avoids
      # hardcoding the letters here.
      @counts = Hash.new(0)
      dna_validation
    end

    def count(element)
      # Renamed to be active, and take a param. There's no reason to
      # save this as an instance variable, as it isn't "long-term"
      # state.
      validate_element(element)
      # No reason to sort the letters, as it shouldn't change the
      # result, and only will take more time. It's also confusing to
      # someone else reading it, as they have to decide if it's
      # important. No reason to be an instance variable.
      @string.chars.count(element)
      # @string.chars /could/ be saved, as it will always be the same,
      # and /might/ save some processing time.
    end

    def nucleotide_counts
      # Ditto sorting and saving the value, especially as it's used
      # in multiple places.
      nucleotides = @string.chars.sort
      nucleotides.each do  |nucleotide|
        @counts[nucleotide] += 1
      end
      @counts
      # This instance variable will be saved between multiple calls to
      # this method, and continue to accumulate. I'd expect the answer
      # to be the same each time.
    end

    def dna_validation
      # You don't have to return a value. This can be written as just
      return if @string.empty?
      raise ArgumentError, "DNA is not RNA" if @string.include?('U')
      raise ArgumentError, "This is not a DNA" unless @string.match(/[ACGT]/)
    end

    def validate_element(element)
      raise ArgumentError, "There are no such nucleotides" unless element.match(/[ACGTU]/)
    end
  end
end