Can I use RSpec to mock stdin/stdout to test console reads & writes?

Question

My Ruby program reads lines from stdin and uses puts to print to stdout (the terminal). Can I use RSpec to test the reads and writes? Can I inject a string to my program like it was written in stdin and at the same time check the output?

line = STDIN.read.chomp.split

Also, I have the reads and writes in a loop, until line[0] is "quit". Can I test while the loop is running or should I call subject.read_in and subject.write_out?

Answer 1

You can use mocks and have the method called more than once by listing multiple values in the and_return() method. These will be returned, one on each call, in the order given.

STDIN.should_receive(:read).and_return("Your string")

STDIN.should_receive(:read).and_return("value1", "value2", "value3")

You can do similar things with STDOUT:

STDOUT.should_receive(:puts).with("string")

See the RSpec mocking documentation for more information.

Answer 2

RSpec 3.0+

With RSpec 3.0, there is output matcher for this purpose:

expect { my_method }.to output("my message").to_stdout
expect { my_method }.to output("my error").to_stderr