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Testing JavaScript with PhantomJS

#391 Testing JavaScript with PhantomJS pro

Nov 07, 2012 | 10 minutes | Testing, Tools, Plugins
PhantomJS allows us to test JavaScript without going through a browser window. Here I show how to do this using Capybara and Poltergeist. I also give some tips on handling database transactions and skipping javascript tests.
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Lukas Svoboda over 4 years ago

Thanks for this episode.
In the scrolling test case, I didn't catch how it works under the hood. As I understand it correct, the content "Order #11" is not present immediately after calling page.evaluate_script("window.scrollTo(0, document.height)").
Does this command wait for the content? If so, how should I test that message "Fetching more orders..." is showed (just for a while)?

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Robert Huberdeau over 4 years ago

Capybara automatically waits for the content to appear. There's a default time it will wait that you can override. I'm not sure how you would reliably test for the "Fetching more orders.." part though. I'm betting that you would run into instances where that disappeared before Capybara could verify it was there.

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Ryan Schmukler over 4 years ago

In case anyone is curious on how this performs against Capybara-webkit as the driver, I found it to be ~10% faster. Additionally, the error messages are much more helpful.

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bjer over 4 years ago

for me Capybara-webkit is around 10 % faster than Phantom and capybara-webkit reports fewer false positives..

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Bruno Bonamin over 4 years ago

Hey Ryan, great episode. Have you tried capybara-webkit? How does PhantomJS compare to this gem? We've been using it extensively and it works pretty well.

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Paul Pettengill over 4 years ago

The advantages I've noticed for poltergeist over capyabara-webkit as the javascript_browser for capybara are:

  1. Poltergeist's errors are a bit more detailed, and that can help with debugging.
  2. Poltergeist allows you set cookies
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Samnang Chhun over 4 years ago

PhantomJS 1.7 doesn't depends on QT as well.

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Andreas Boehrnsen over 4 years ago

like Samnang already said, it does not depend on QT.

For us it was quite a pain to get Capybara Webkit running because of the QT dependencies. I can also remember some compilation issues on CentOS.
So Poltergeist came as god sent. It is a nice small package that is "just working".

If you have Capybara Webkit running and are happy with it you probably do not need to switch.

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Jean-Philippe Boily over 4 years ago

I've made some short testing and capybara-webkit is still around 20% faster in our use case. I suggest you try it for yourself and see, that's a matter of minutes or hours if run longer tests to have better metrics.

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Herby Raynaud over 4 years ago

Great work again Ryan.

I starting using this on my latest project and it rocks. However beware of bug related to following relative urls.

Phantomjs is unable to follow a javascript redirect (i.e. window.location.href = XXX"
it throws a "Not allowed to load local resource" error.

AS a quick and dirty i just changed the relative url to full url in the affected code and that fixed the problem.

Hope that helps anyone that might encounter this issue.

Here is link to recent post with some specific issue tix

https://groups.google.com/forum/?fromgroups=#!topic/phantomjs/fVBd3kGOQh4

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Nicolai Seerup over 4 years ago

I´m getting an Dead::Client error with phantomjs. I think it´s an issue when using fontawesome webfonts. Has anyone a solution to that?

https://github.com/jonleighton/poltergeist/issues/44

https://gist.github.com/3996516

https://gist.github.com/4003597

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Sergey Kuleshov over 4 years ago

Found a very weird bug, maybe it is actually poltergeist related. While I haven't had time to fully investigate it here is what happens:

ruby 
visit root_path
.. here I do routine to login as a valid user, which works...
visit protected_area_path

boom, after the second visit I find that that I am logged out, current_user is nil.

If, on the other hand instead of doing the second visit call I use respective click_link sequence everything works like a charm.

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Brandon over 4 years ago

I did just a little bit of testing, but for me PhantomJS was about 20% slower than Capybara-Webkit.

You don't end up with the QT dependency though... So that might be worth its weight in gold to some.

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alejomongua over 4 years ago

I get this error when i try to run the specs:

console 
Exception encountered: #<LoadError: cannot load such file -- capybara/poltergeist>
backtrace:

What could that be for?

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HuckyDucky about 4 years ago

This doesn't work for me. All "page.should have_content" assertions fail under this stack. And when I do a "save_and_open_page", well, there's no styling and no JS. In other words, there's nothing available from the asset pipeline. It has been a real struggle. 5 12-hour days straight trying to set up this testing stack. What a waste.

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HuckyDucky about 4 years ago

FactoryGirl fails with:

undefined method `error_field' for nil:NilClass

No stack trace given, naturally.

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HuckyDucky about 4 years ago

I was getting a "PG::Error connection closed" message. Here is the solution:

For Postgres users who are also using Spork, the Plataformatec blog solution will not work as stated. In other words, if you put the shared_db_connection.rb file in your spec/support directory, you will get a PG::Error connection closed message. Leave the file in spec/support but remove this line:

ActiveRecord::Base.shared_connection = ActiveRecord::Base.connection
And instead put that in your Spork.each_run block in your spec_helper.rb file.

H/T nicholasmott from the comments section on the Plataformatec blog.

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Jonathan Kirst almost 4 years ago

This is a life saver! Thanks for the tip.

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railscastuser about 4 years ago

Does anybody know of a way to run your js specs at the and of the suite?!

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