Module to Flatten Arrays

gistfile1.txt

#
# flattener.rb
#
module Flattener
  class ::InvalidInputError < StandardError; end

  def self.execute(array)
    raise InvalidInputError unless can_be_flattened?(array)

    process(array)
  end

  private

  def self.can_be_flattened?(object)
    object.is_a? Array
  end

  def self.process(array)
    sum = []

    array.each do |obj|
      sum += can_be_flattened?(obj) ? process(obj) : [obj]
    end

    sum
  end
end

#
# flattener_spec.rb
#
require_relative 'flattener.rb'

RSpec.describe Flattener do
  describe ".execute" do
    context "given an array" do
      it "returns empty array from empty array" do
        expect(subject.execute([])).to eq []
      end

      it "returns the same array given a one level array" do
        flat_array = [1,2,3]
        expect(subject.execute(flat_array)).to eq flat_array
      end

      it "returns a flat array given a multi level array" do
        leveled_array = [1, [2], [3,4,[5]]]

        expect(subject.execute(leveled_array)).to eq [1,2,3,4,5]
      end

      it "returns a flat array given non-integer contents" do
        leveled_array = [{}, ["A"], [3,4,[5], [6,[7]]]]

        expect(subject.execute(leveled_array)).to eq [{},"A",3,4,5,6,7]
      end
    end

    context "given a non-array" do
      it "returns InvalidInputError" do
        expect{ subject.execute({}) }.to raise_error InvalidInputError
      end
    end
  end
end