Flatten a nested array

arr_flatten.rb

module ArrFlatten
    # Public: Returns a flat array
    #
    # nested_array  - A nested array
    #
    # Examples
    #  nested_array = [ [1,2,3], [4,5,6], [7,8,9] ]
    #  ArrFlatten.arr_flatten(nested_array)
    #  => [1, 2, 3, 4, 5, 6, 7, 8, 9]
    #
    # Returns array
  def self.arr_flatten(nested_array)
    return [] unless nested_array.is_a?(Array)
    nested_array.each_with_object([]) do |element, flattened|
        flattened.push *(element.is_a?(Array) ? arr_flatten(element) : element)
    end
  end
end

arr_flatten_spec.rb

require 'arr_flatten'

describe ArrFlatten do

  let(:flat_array) { [1, 2, 3, 4, 5, 6, 7, 8, 9] }
  let(:nested_example_1) { [ [1,2,3], [4,5,6], [7,8,9] ] }
  let(:nested_example_2) { [ [1,2,3], 4,5,6, [7,8,9] ] }
  let(:nested_example_3) { [ [1,2,3], 4,5,6, [7,[8,9]] ] }

  describe '.arr_flatten(array)' do
    context 'given no arguments' do
      it 'should raise an ArgumentError' do
        expect { subject.arr_flatten }.to raise_error ArgumentError
      end
    end

    context 'given invalid arguments' do
      context 'given a non-array' do
        it 'should not raise an error' do
          expect { subject.arr_flatten "not_an_array" }.not_to raise_error
        end

        it 'should return an empty array' do
          a = subject.arr_flatten "not_an_array"
          expect(a).to eq []
        end
      end

      context 'given an empty array' do
        it 'should return an empty array' do
          a = subject.arr_flatten []
          expect(a).to eq []
        end
      end
    end

    context 'given valid arguments' do
      it 'should not throw an error' do
        expect { ArrFlatten.arr_flatten flat_array }.not_to raise_error
      end

      context 'given a flat array' do
        it 'should not alter the array' do
          expect(subject.arr_flatten flat_array).to eq(flat_array)
        end
      end

      context 'given an arbitrarily nested array' do
        it 'should return an flat array' do
          expect(subject.arr_flatten nested_example_1). to eq(flat_array)
          expect(subject.arr_flatten nested_example_2). to eq(flat_array)
          expect(subject.arr_flatten nested_example_3). to eq(flat_array)
        end
      end
    end
  end
end

output.txt

⇒  rspec

ArrFlatten
  .arr_flatten(array)
    given no arguments
      should raise an ArgumentError
    given invalid arguments
      given a non-array
        should not raise an error
        should return an empty array
      given an empty array
        should return an empty array
    given valid arguments
      should not throw an error
      given a flat array
        should not alter the array
      given an arbitrarily nested array
        should return an flat array

Finished in 0.00344 seconds (files took 0.09457 seconds to load)
7 examples, 0 failures