Ruby implementation of 'flatten'

flatten.rb

=begin rdoc
Takes any nested combination of Arrays and returns their contents as a
single Array. my_flatten(nil) returns an empty Array.
=end

def my_flatten values=[]
  raise "`my_flatten' requires an Array argument." unless values.is_a?(Array)

  result = []
  values.each do |v|
    if v.is_a?(Array)
      result.concat my_flatten(v)
    else
      result << v unless v.nil?
    end
  end

  result
end

if __FILE__ == $0
  require 'minitest/autorun'
  require 'minitest/pride'

  class MyFlattenTest < MiniTest::Unit::TestCase
    def test_flattens_to_arbitrary_depth
      result = my_flatten([1, [2, 3], 4, [[5, 6, [7], 8], 9, 10], 11])

      assert_equal [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], result
    end

    def test_raises_exception_when_passed_non_array
      assert_raises RuntimeError do
        my_flatten(a: 1, b: [2])
      end
    end

    def test_eliminates_empty_arrays
      result = my_flatten([1, [], 2, [3]])

      assert_equal [1, 2, 3], result
    end

    def test_eliminates_nils
      result = my_flatten([1, nil, 3])

      assert_equal [1, 3], result
    end

    def returns_an_empty_array_when_called_with_no_argument
      assert_equal [], my_flatten
    end
  end
end