ruby - Test output to command line with RSpec

Question

I want to do is run ruby sayhello.rb on the command line, then receive Hello from Rspec.

I've got that with this:

class Hello
  def speak
    puts 'Hello from RSpec'
  end
end

hi = Hello.new #brings my object into existence
hi.speak

Now I want to write a test in rspec to check that the command line output is in fact "Hello from RSpec" and not "I like Unix"

NOT WORKING. I currently have this in my sayhello_spec.rb file

require_relative 'sayhello.rb' #points to file so I can 'see' it

describe "sayhello.rb" do
  it "should say 'Hello from Rspec' when ran" do        
    STDOUT.should_receive(:puts).with('Hello from RSpec')    
  end
end

Can someone point me in the right direction please?

Answer 1

Here's a pretty good way to do this. Copied from the hirb test_helper source:

def capture_stdout(&block)
  original_stdout = $stdout
  $stdout = fake = StringIO.new
  begin
    yield
  ensure
    $stdout = original_stdout
  end
  fake.string
end

Use like this:

output = capture_stdout { Hello.new.speak }
output.should == "Hello from RSpec
"