How to test puts in 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
         


        

Answer 1

Somewhat similar to bswinnerton's answer, one can capture puts output and then test against the captured output, without having to use the library-dependent capture method (which someone has mentioned is being deprecated in Rails 5).

Ruby has a global variable named $stdout which by default is populated by the constant STDOUT. STDOUT is that which sends data to the ruby process's stdout stream (not sure if "stream" is the right term here). Basically in a naive case STDOUT.puts("foo") will result in "foo\n" appearing in your terminal window. $stdout.puts("foo") will do the same thing because the $stdout variable name refers to STDOUT unless you reassign it (key point here). Finally puts("foo") is syntactic sugar for $stdout.puts("foo").

The strategy then is to reassign $stdout to a local IO instance which you can inspect after running your code, to see if "Hello from RSpec" showed up in its contents.

How this would work:

describe "sayhello.rb" do
  it "should say 'Hello from Rspec' when ran" do        
    $stdout = StringIO.new

    # run the code
    # (a little funky; would prefer Hello.new.speak here but only changing one thing at a time)
    require_relative 'sayhello.rb' 

    $stdout.rewind   # IOs act like a tape so we gotta rewind before we play it back  

    expect($stdout.gets.strip).to eq('Hello from Rspec')
  end
end