count_by_word.rb

# Example Answer to http://qiita.com/jnchito/items/c4a56046be1096c19b1c

def count_by_word(str)
  raise ArgumentError, 'str should be a string' unless str.is_a? String

  str.split.reduce(Hash.new(0)) {|rs, w| rs.merge(w => rs[w] + 1) }
end

describe "count_by_word" do
  let(:results) { count_by_word(string) }

  context 'given a normal string' do
    let(:string) { "no ruby no life" }

    it { expect(results).to eq('no' => 2, 'life' => 1, 'ruby' => 1) }
  end

  context "given a multiple-line string" do
    let(:string) { "no ruby no life\nwe love ruby\n" }

    it { expect(results).to eq('no' => 2, 'life' => 1, 'ruby' => 2, 'we' => 1, 'love' => 1) }
  end

  context "given a string with leading or trailing spaces" do
    let(:string) { "  no ruby no life  " }

    it { expect(results).to eq('no' => 2, 'life' => 1, 'ruby' => 1) }
  end

  context "given an empty string" do
    let(:string) { "" }

    it { expect(results).to eq({}) }
  end

  context "given a string made up of spaces" do
    let(:string) { "   " }

    it { expect(results).to eq({}) }
  end

  context "given nil" do
    let(:string) { nil }

    it { expect { count_by_word(string) }.to raise_error ArgumentError }
  end
end