This is an Array instance method that flattens any kind of array or array of arrays that contain integers (Fixnum)

flatten_ints

require 'rspec'
class Array

  def flatten_ints(all=[])
    self.each do |item|
      if item.class == Array
        item.flatten_ints(all)
      else
        unless item.class == Fixnum
          raise TypeError.new "This Methos is only for flattening Fixnums"
        end
        all << item
      end
    end
    all
  end

end

module ArraySpecHelper

  def array(n)
    n
  end

  def array_of_array(n)
    [n]
  end

  def array_of_array_of_array(n)
    [[n]]
  end

  # this helper method can be called with an array of one or all of the preset variables
  # it iterates over 20 times and calls send on the current sampled bag. 
  # one can call array_types([:array]) and expect a simple array
  # calling it with all three will give you a sample of all types
  def array_types(bag = %i[array array_of_array array_of_array_of_array])
    (1..20).to_a.map{ |n| send(bag.sample, n) }
  end

end

describe Array do
  include ArraySpecHelper

  context "flatten_ints" do

    context 'success' do 
      it "keeps an already flattened array the same" do
        # array_types([:array]).flatten_ints.each do |n|
        #   expect(n.class).to eq(Fixnum)
        # end
        expect(array_types([:array]).flatten_ints).to eq((1..20).to_a)
      end
    
      it "flattens out an array of arrays" do
        expect(array_types([:array_of_array]).flatten_ints).to eq((1..20).to_a)
      end

      it "flattens out an array of array of arrays" do
        expect(array_types([:array_of_array_of_array]).flatten_ints).to eq((1..20).to_a)
      end

      it "flattens out a mixed bag of arrays" do
        expect(array_types.flatten_ints).to eq((1..20).to_a)
      end
    end

    context 'failure' do 
      it "only works for integers" do
        expect { %w[a b 3].flatten_ints }.to raise_error(TypeError, 'This Methos is only for flattening Fixnums')
      end
    end

  end

end

Any code after the raise won’t be executed

Oops looking on my phone. Consider restructuring that line to be shorter or put the unless on the line above