Function to flatten an array

.rspec

--format documentation
--color
--require spec_helper

flatten.rb

class Flatten
  def flatten(array)
    array.each_with_index do |item, index|
      array.insert(index, *array.delete(item))
    end
  end
end

flatten_spec.rb

RSpec.describe Flatten do 
  describe "#flatten" do 
    context "array is already flat" do 
      let(:arr) { [ 1 ] }

      it "returns the array unchanged" do 
        expect(subject.flatten(arr)).to eq arr
      end
    end

    context "array with sub-array" do 
      let(:arr) { [ [ 1 ] ] }

      it "returns the array flattened" do 
        expect(subject.flatten(arr)).to eq arr.flatten
      end
    end

    context "longer array with sub-array" do 
      let(:arr) { [ 1, [ 2 ], 3, 4 ] }

      it "returns the array flattened" do 
        expect(subject.flatten(arr)).to eq arr.flatten
      end
    end

    context "multiple items in sub-array" do 
      let(:arr) { [ 1, [ 2, 3 ], 4 ] }

      it "returns the array flattened" do 
        expect(subject.flatten(arr)).to eq arr.flatten
      end
    end

    context "nested sub-arrays" do 
      let(:arr) { [ 1, [ 2, [ 3 ] ], 4 ] }

      it "returns the array flattened" do 
        expect(subject.flatten(arr)).to eq arr.flatten
      end
    end
  end
end

spec_helper.rb

require_relative "../flatten"