When You Don't Know, Test

Two articles in one night! Wow, you are lucky, eh? Anyway, I figured the first post, on Gmail wouldn’t be as applicable for everyone, so I thought I would hit on something new I’ve been doing of late for the rest of you. What you ask? Well, lately, when I don’t know how something works or I’m not sure what the outcome of something is going to be, I run it quick in IRB or make a small test case for it.

IRB

If it is something small enough that I can run on one line, I’ll just open it up in IRB and see what happens. Take for example the other day. I was trying to remember how to use regular expression matches in the gsub replace string, so I fired up IRB and tried what I thought was right.

$ irb
>> </code><code class="ruby">'foobar'.gsub(/^foo(bar)/, '\1')</code><code>
=> "bar"

That quick, I knew that I had guessed right and could move on in the project I was working on. Sure, I could have just guessed inside my project, but I find more isolated examples like this outside of a project help cement things in my head better.

Test Case

Now for small things, IRB works great, but for larger things, I find it better to make a quick test case. The other day, I was wondering how capable Time#parse was so I created the following test case.

require 'test/unit'
require 'time'

class TestTimeParse < Test::Unit::TestCase
  def test_parsing_verbosely
    assert_equal(3, Time.parse('3am').hour)
    assert_equal(15, Time.parse('3pm').hour)
    assert_equal(3, Time.parse('3 am').hour)
    assert_equal(15, Time.parse('3 pm').hour)

    assert_equal(3, Time.parse('3a.m.').hour)
    assert_equal(15, Time.parse('3p.m.').hour)
    assert_equal(3, Time.parse('3 a.m.').hour)
    assert_equal(15, Time.parse('3 p.m.').hour)
    
    assert_equal(3, Time.parse('3AM').hour)
    assert_equal(15, Time.parse('3PM').hour)
    assert_equal(3, Time.parse('3 AM').hour)
    assert_equal(15, Time.parse('3 PM').hour)
    
    assert_equal(3, Time.parse('3A.M.').hour)
    assert_equal(15, Time.parse('3P.M.').hour)
    assert_equal(3, Time.parse('3 A.M.').hour)
    assert_equal(15, Time.parse('3 P.M.').hour)
  end
end

All 16 assertions passed and I had my answer. It only takes a second to create a new document in TextMate, require ‘test/unit’ and create a test case. I’ve started creating test cases like this for a lot of things.

Store the Test Cases

Not only do I create these test cases, but I also save them all in a directory. This means whenever I want to relearn something that I have most likely forgotten, I have a directory full of fun test cases to check out. Next time you think, “I wonder”, go ahead and try it out for yourself. I’m also curious what you do for things like this. Anyone else do something similar? Better?

9 Comments

V-t
Dec 12, 2008

you’ve just tested Time.parse in YOUR app
grosser
Dec 12, 2008

i am definitely using irb for all these small tests,
but most of the time, making those ‘fun tests’ does not seem worthwhile,
because in doubt ill never find them again…
(i do not think/hope it was suggested that these fun tests should be kept in the app tests, just somewhere else)
Jon Wood
Dec 12, 2008

V-t: I think you’re missing the point a bit here – they’re not tests that become a part of the applications test suite, it’s just a handy way to quickly verify that your assumptions about a particular library are correct.
Don
Dec 12, 2008

I do the same thing as far as little tests scripts, I have a “playground” directory littered with all manner of small experiments.

As for irb, I really recommend the Utility Belt gem if you haven’t heard of that. It requires wirble, so you get the syntax highlighting and tab completion, along well as auto-indenting of blocks/methods. Plus some other more advanced bells and whistles of various usefulness.
John Nunemaker
Dec 12, 2008

@V-t – Yep, the others are correct. I’m not talking about app tests. I’m more talking about a “playground” as Don mentioned.
Brian LeRoux
Dec 13, 2008

Hah! Cool, yep I do this very same thing. Love IRB (and Utility Belt is must have .irbrc fu) but if you really want to test your assumptions a quick test case is the way to go. Been doing more benchmark requires of late too.

Good post John — wonder if a shared repo of these sorts of tests wouldn’t be a cool resource?
David Vrensk
Dec 14, 2008

It only takes a second to create a new document in TextMate, require ‘test/unit’ and create a test case.

That’s so true. Especially if you know that typing “tc” and hitting tab gives you a skeleton.

(It strikes me that it would be useful if TextMate supported “a tip a day” hooks in its bundles. There are so many features that I’ve only found out about after a long while, and presumably tons that I haven’t found yet.)
John Nunemaker
Dec 14, 2008

David - Oh, wow. Overlooked that shortcut somehow. Thanks for the tip. I do use the @deft shortcut to quickly create a test method, but I was unaware of the tc shortcut. Very nice!
Matthew Lang
Dec 20, 2008

Great article John. I wish I thought of this years ago.

Keeping a library of tests to validate your understanding of a framework is a great way to learn the framework and at the same time, provide yourself with examples on how to use that framework correctly.