…is best done very carefully, and with the knowledge that not everything works as you'd like it do. That's a good metaphor for my week this week.
Working on our new platform and its (eventual) variety of products and supporting tools, mostly in Ruby using Rails, some of the absolutely key elements are primarily front-end code, written as CoffeeScript running in the browser. Typically enough, we make heavy use of jQuery, various plugins, and other libraries. When understood and used correctly and they work as expected, they're great for reducing the effort needed to accomplish new and useful things.
The moderately-sized application I'm presently working on uses over 125 third-party components, many of which are dependencies of components we directly/intentionally use. Of those, some three dozen components have yet to reach a "1.0" release level. That's a lot of trust we put into people we've never met and teams completely outside our organisation. The fact that this is typical to the point of being mundane among Ruby shops is one of the phenomena most commonly cited by new Ruby devs and managers as "mind-blowing".
When everything works properly, it's awesome in a very different way than anything I've done in my nearly 35-year career. When anything fails to work properly, it's equally spectacular; just in a very different way.
Consider today. I've been working on a Script component (which I expect to publish in due course as a jQuery plugin itself). Being a proper behaviour-driven development project, I've been writing specs using Mocha and running them with Teaspoon. Teaspoon lets you run your spec suite either in a browser or from the command line. The browser-based interface is easy and convenient (almost fun) to work with during development; with a mouse click, you can focus on just the spec you're working with at the moment, or step back and run a group of related specs or your entire suite. After finally finding and killing the last of never-mind-how-many typos and silly errors (CoffeeScript, alas, has not yet implemented proper DWIM support), I had the component working. It was clean. It was more than fast enough for my purposes. And, most importantly, it worked properly, against every condition I threw at it.
That is, when I was running Teaspoon from the browser. The command-line invocation, needed for continuous integration among other things, failed in a very odd fashion. See, for example, this bit of screen output:
[jeffdickey@Jeffs-Prolog-iMac select_demo (wip)]$ teaspoon -q | tapout
Started w/ Seed: 0
..................F
1. FAIL markup from selectedMarkup()
Unknown
TypeError: 'undefined' is not a function (evaluating 'currentNode.contains(last)') in http://127.0.0.1:58247/assets/selection_wrapper.js?body=1 (line 111)
window.meldd.SelectionWrapper for rich single-paragraph content, returns the correct markup from selectedMarkup().#:0
Finished in 0.092s (206.522 test/s, 0.004842s avg.)
19 tests: 18 pass, 1 fail, 10 exit, 0 todo, 0 omit
Now, bear in mind that when Teaspoon was running inside the browser, no such error message was displayed; all specs passed. The code being complained about looked something like:
getMarkupUntil: (currentNode, contentString, last, offset) ->
while currentNode?
if currentNode.contains(last) # <-- THIS IS THE LINE BEING COMPLAINED ABOUT
if currentNode == last
# do something...
else # currentNode contains last but is not last
# do something else...
else # currentNode does not contain last but we're still looking
# do something different...
# return our results
Now, currentNode.contains is making use of a bog-standard HTML DOM function that's been in every major browser for years. Even Internet Exploder 5, from the Dark Ages of 1999, managed to support it! What could possibly go wrong?!?
Tap dancing on the shoulders of not-always-giants, it turns out.
Teaspoon, by default, uses PhantomJS as a "headless Webkit browser workalike with JavaScript support". If you're going to automate testing of your Web-based application (or any of several other related activities), this is the tool you want to use. Except, o course, when it doesn't work correctly. I changed the getMarkupUntil method I showed earlier to test my hunch:
getMarkupUntil: (currentNode, contentString, last, offset) ->
while currentNode?
return null unless currentNode.contains?
if currentNode.contains(last) # <-- THIS IS THE LINE BEING COMPLAINED ABOUT
if currentNode == last
# do something...
else # currentNode contains last but is not last
# do something else...
else # currentNode does not contain last but we're still looking
# do something different...
# return our results
The new line returns a null value from the function if and only if currentNode has no property (data or method) named contains. I reasoned that this would (fairly obviously) cause the calling code to fail, and the difference in the failure message (from what was shown previously) would confirm to me that this was indeed the problem. Again, running the specs from inside the browser presented no problems. Running from the command line, however, yielded
[jeffdickey@Jeffs-Prolog-iMac select_demo (wip)]$ teaspoon -q | tapout
Started w/ Seed: 0
..................F
1. FAIL markup from selectedMarkup()
Unknown
TypeError: Type error in http://127.0.0.1:58271/assets/selection_wrapper.js?body=1 (line 174)
window.meldd.SelectionWrapper for rich single-paragraph content, returns the correct markup from selectedMarkup().#:0
Finished in 0.090s (211.111 test/s, 0.004737s avg.)
19 tests: 18 pass, 1 fail, 10 exit, 0 todo, 0 omit
As expected, the null value caused other code to die.
I then browsed the Teaspoon documentation, which pointed out that although PhantomJS was used by default, Selenium could be used instead, by installing the selenium-webdriver Gem and updating the project configuration accordingly. After re-bundling the app, I could run my spec suite from the command line. Hurrah!
Well, golf-clap applause at least. We'd had previous problems with Selenium testing the Script code as run from within a Web app. We'll burn that bridge again when it falls on us. Again.
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