コンソールに文字を出力する処理を検証する

test_console_output_by_rspec.rb

require "stringio"

def capture(stream)
  begin
    stream = stream.to_s
    eval "$#{stream} = StringIO.new"
    yield
    result = eval("$#{stream}").string
  ensure
    eval "$#{stream} = #{stream.upcase}"
  end
  result
end

describe Foo do
  it "output should be 'bar'" do
    output = capture(:stdout) do
      baz # test method
    end
    expect(output).to eq 'bar'
  end
end