# Visibility in tests **URL:** \ **Category:** Ruby\ **Created:** [April 7, 2010, 2:26am UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429 "2010-04-07T02:26:17Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 7, 2010, 2:26am UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429/1 "2010-04-07T02:26:17Z")
Hi, I’m new to this, forum, but I really love Ruby and I hope this is the right place to discuss problems and questions I have. I learned Ruby when I was twelve, so I know Ruby for more than one third of my life and I now call it my “mother tongue” of programming languages, but I mostly programmed rather childish stuff and for a long time, I was not interested in learning more than the basic stuff, since I could just do everything I wanted with that already. However, in the last few months, my Ruby programming has grown a little more serious, and (among other things) I started for example to write tests for all of my programs that included more than 100 lines, even for private purposes. Usually that went quite well, but there stumbling block in my way that annoyed me multiple times, so I decided to ask some people who maybe know a little more about Ruby. I don’t know how to apply unit tests to private methods. Usually, I only use very few private methods and for my small private purposes, it was okay to just set those few to public, too, but how do you do that in a good way, if you really do have good reasons for making the methods private? Another small question: Do you know where I can find Ruby style guidelines or something like that? ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 7, 2010, 2:43am UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429/2 "2010-04-07T02:43:28Z")
On Apr 6, 2010, at 17:26 , Bernhard B. wrote: > I don’t know how to apply unit tests to private methods. Usually, I only > use very few private methods and for my small private purposes, it was > okay to just set those few to public, too, but how do you do that in a > good way, if you really do have good reasons for making the methods > private? easy! make them public! Either don’t make them private in the first place (my preference) or make them public in your tests (second choice… usually when I’m working with inherited code): class X public :previously\_private\_method end class TestX \< MiniTest::Unit::TestCase def test\_previously\_private\_method … end end ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 7, 2010, 11:11am UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429/3 "2010-04-07T11:11:49Z")
Ryan D. wrote: > On Apr 6, 2010, at 17:26 , Bernhard B. wrote: > > > I don’t know how to apply unit tests to private methods. Usually, I only > > use very few private methods and for my small private purposes, it was > > okay to just set those few to public, too, but how do you do that in a > > good way, if you really do have good reasons for making the methods > > private? > > easy! make them public! Or use one of: obj.send(:private\_method\_name, args…) obj.instance\_eval { private\_method\_name args… } Note that the latter also switches the object context so that ‘@foo’ inside the block means the @foo instance variable inside obj. That can be useful too. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 7, 2010, 12:54pm UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429/4 "2010-04-07T12:54:00Z")
Ryan D. wrote: > On Apr 6, 2010, at 17:26 , Bernhard B. wrote: > > > I don’t know how to apply unit tests to private methods. Usually, I only > > use very few private methods and for my small private purposes, it was > > okay to just set those few to public, too, but how do you do that in a > > good way, if you really do have good reasons for making the methods > > private? > > easy! make them public! > > Either don’t make them private in the first place (my preference) or > make them public in your tests (second choice… usually when I’m > working with inherited code): > > class X > public :previously\_private\_method > end > > class TestX \< MiniTest::Unit::TestCase > def test\_previously\_private\_method > … > end > end Okay, thanks, a lot, nice and easy idea, I should have seen that. 🙂 Brian C. wrote: > Ryan D. wrote: > > > On Apr 6, 2010, at 17:26 , Bernhard B. wrote: > > > > > I don’t know how to apply unit tests to private methods. Usually, I only > > > use very few private methods and for my small private purposes, it was > > > okay to just set those few to public, too, but how do you do that in a > > > good way, if you really do have good reasons for making the methods > > > private? > > > > easy! make them public! > > Or use one of: > > obj.send(:private\_method\_name, args…) > > obj.instance\_eval { private\_method\_name args… } > > Note that the latter also switches the object context so that ‘@foo’ > inside the block means the @foo instance variable inside obj. That can > be useful too. Thanks a lot, I think the possibility to access instance variables from outside will also be very useful for other purposes. Okay, now I will have no problems anymore to write tests for private methods.^^ ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 8, 2010, 2:33am UTC](https://www.ruby-forum.com/t/visibility-in-tests/186429/5 "2010-04-08T02:33:32Z")
I’m going to guess that I’m the odd one out here, but… On Tuesday 06 April 2010 07:26:20 pm Bernhard B. wrote: > I don’t know how to apply unit tests to private methods. Usually, I only > use very few private methods and for my small private purposes, it was > okay to just set those few to public, too, but how do you do that in a > good way, if you really do have good reasons for making the methods > private? Don’t test them directly. Well, alright, let me take a step back: I agree with Ryan here that they shouldn’t be private at all. In a language like Java, I can understand, but in Ruby, your users will have the source code, and even if they don’t, they’ll have Object#send and instance\_variable\_get/set. Your best bet is to explicitly document your public API. If people use methods that aren’t documented, they get to keep both pieces. However, there are exceptions – if I recall, Rails will automatically make certain methods inaccessible to mass assignment if they’re private or protected. Anyway… Presuming you really do have a good reason for making them private, you probably have an even better reason to not unit test them directly, and certainly not to rely on the state of instance variables in your unit tests. Your tests should verify _behavior_, not the minute details of _state_. As an example: I realize this is about the worst way to do things, but let’s pretend you have the following methods on Integers: public def is\_prime? factors.empty? end private def factors # … end Now, your tests should be testing _what_ you actually care about, not _how_ it’s implemented. So, instead of testing factors directly, you would test is\_prime. Your tests would look something like this: it ‘should believe 4 is prime’ 5.should be\_prime 4.should\_not be\_prime … end I realize this makes them more integration tests than unit tests, and maybe I’m missing the point, but I just don’t see the use of such fine-grained tests. You want them fine-grained enough to actually catch bugs, but coarse enough that they’re actually worth writing.