require 'spec_helper'

describe Immutable::List do
  describe '#combination' do
    it 'is lazy' do
      -> { Immutable.stream { fail }.combination(2) }.should_not raise_error
    end

    [
      [%w[A B C D], 1, [L['A'], L['B'], L['C'], L['D']]],
      [%w[A B C D], 2, [L['A','B'], L['A','C'], L['A','D'], L['B','C'], L['B','D'], L['C','D']]],
      [%w[A B C D], 3, [L['A','B','C'], L['A','B','D'], L['A','C','D'], L['B','C','D']]],
      [%w[A B C D], 4, [L['A', 'B', 'C', 'D']]],
      [%w[A B C D], 0, [EmptyList]],
      [%w[A B C D], 5, []],
      [[], 0, [EmptyList]],
      [[], 1, []],
    ].each do |values, number, expected|
      context "on #{values.inspect} in groups of #{number}" do
        let(:list) { L[*values] }

        it 'preserves the original' do
          list.combination(number)
          list.should eql(L[*values])
        end

        it "returns #{expected.inspect}" do
          list.combination(number).should eql(L[*expected])
        end
      end
    end
  end
end
