Rspec with Ruby basic output String testing raises an error -

i've tried write basic test rspec, in order test reception of string on standard output.

i've stubed standard output same way it's written in rspec book :

require './tweetag.rb'   module tweetag    describe tweet     describe "#print"       "prints test"         output = double('output').as_null_object         t = tweetag::tweet.new(output)         t.print         output.should_receive(:puts).with('test')    end   end  end  end 

the ruby code looks :

module tweetag   class tweet     def initialize(output)       @output=output     end      def print       @output.puts('test')     end    end end 

as can see, nothing complicated. still, answer receive after running specs following :

failures:    1) tweetag::tweet#print prints test      failure/error: output.should_receive(:puts).with('test')        (double "output").puts("test")            expected: 1 time            received: 0 times 

i've tried removing "as_null_object" , answer :

  1) tweetag::tweet#print prints test      failure/error: t.print        double "output" received unexpected message :puts ("test") 

thank help.

the should_receive method has used before calling method.

output = double('output').as_null_object t = tweetag::tweet.new(output) output.should_receive(:puts).with('test') t.print 

as side note, test missing check on return value here. know print method doesn't raises exception. don't check return value appropriate.

output.should_receive(:puts).with('test').and_return('returned value') t.print.should eql('returned value')