There's two solutions: redirecting where puts writes to (the solution given by @cldwalker above), or overwriting the puts method itself to be a no-op. (The implementation should be obvious: module Kernel; def puts(*args) end end).
However, in this case, what would really be the best solution is "listening to your tests". Because, oftentimes when something is awkward to test, your tests are really trying to tell you that something is wrong with your design. In this case, I smell a violation of the Single Responsibility Principle: why the heck does a Model object need to know how to write to the console? Its responsibility is representing a Domain Concept, not logging! That's what Logger objects are for!
So, an alternative solution would be to have the Model object delegate the responsibility for logging to a Logger object, and use dependency injection to inject the Model object with a suitable Logger object. That way, you can simply inject a fake logger for the test. Here's an example:
#!/usr/bin/env ruby
class SomeModel
def initialize(logger=Kernel) @logger = logger end
def some_method_that_logs; @logger.puts 'bla' end
end
require 'test/unit'
require 'stringio'
class TestQuietLogging < Test::Unit::TestCase
def setup; @old_stdout, $> = $>, (@fake_logdest = StringIO.new) end
def teardown; $> = @old_stdout end
def test_that_default_logging_is_still_noisy
SomeModel.new.some_method_that_logs
assert_equal "bla\n", @fake_logdest.string
end
def test_that_logging_can_be_made_quiet
fake_logger = Object.new
def fake_logger.puts *args; end
SomeModel.new(fake_logger).some_method_that_logs
assert_equal '', @fake_logdest.string
end
end
At the very least, the Model object should take the IO object that it is logging to as an argument, so that you can simply inject StringIO.new into it for the test:
#!/usr/bin/env ruby
class SomeModel
def initialize(logdest=$>) @logdest = logdest end
def some_method_that_logs; @logdest.puts 'bla' end
end
require 'test/unit'
require 'stringio'
class TestQuietLogging < Test::Unit::TestCase
def setup; @old_stdout, $> = $>, (@fake_logdest = StringIO.new) end
def teardown; $> = @old_stdout end
def test_that_default_logging_is_still_noisy
SomeModel.new.some_method_that_logs
assert_equal "bla\n", @fake_logdest.string
end
def test_that_logging_can_be_made_quiet
fake_logdest = (@fake_logdest = StringIO.new)
SomeModel.new(fake_logdest).some_method_that_logs
assert_equal '', @fake_logdest.string
assert_equal "bla\n", fake_logdest.string
end
end
If you still want to be able to just say puts whatever in your Model or you are afraid that someone might forget to call puts on the logger object, you can provide your own (private) puts method:
class SomeModel
def initialize(logdest=$>) @logdest = logdest end
def some_method_that_logs; puts 'bla' end
private
def puts(*args) @logdest.puts *args end
end
