Closest to zero! Just a short program for fun!

closest_to_zero.rb

class Closest
  MAX = 2000000000000

  def to_zero(input)
    raise IllegalArgumentException if input.nil? || input.empty?

    closest_to_zero = MAX
    @least_distance = MAX
    input.each do |num|
      if closer_to_zero(num)
        @least_distance = num.abs 
        closest_to_zero = num
      elsif positive_of_closest_to_zero_exist?(num)
        closest_to_zero = num
      end
    end
    closest_to_zero
  end

  def closer_to_zero(num)
    num.abs < @least_distance
  end

  def positive_of_closest_to_zero_exist?(num)
    num.abs == @least_distance && num > 0
  end

end

class IllegalArgumentException < Exception
end

closest_to_zero_spec.rb

require_relative "closest_to_zero"

describe Closest do
  it "throws IllegalArgumenException when input is nil" do
    lambda do
      subject.to_zero(nil)
    end.should raise_error(IllegalArgumentException)
  end

  it "throws IllegalArgumentException when input is empty" do
    expect do
      subject.to_zero([])
    end.to raise_error(IllegalArgumentException)
  end

  it "returns the only number when there is one element" do
    subject.to_zero([1]).should == 1
  end

  it "returns closer number to zero between 2 numbers" do
    subject.to_zero([2, 1]).should == 1
  end

  it "returns closer nubmer to zero between multiple numbers" do
    subject.to_zero([2, 3, 1, 4]).should == 1
  end

  it "returns negative number which is closer to zero" do
    subject.to_zero([2, -1, 3, 4]).should == -1
  end

  it "returns closest negative number to zero" do
    subject.to_zero([-1, -5, 3, 2]).should == -1
  end

  it "returns positive when negative & positive of same distance to zero exist" do
    subject.to_zero([-1, 1]).should == 1
    subject.to_zero([1, -1]).should == 1
  end

  it "returns the closest number to zero" do
    subject.to_zero([1, -2, 3, -1, -5, 5, 2]).should == 1
  end
end