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Daniel Heath blogs here

Fast tests with PhantomJS

date: 22/08/2011

So, I write (and run) javascript tests a lot.

I run javascript specs by serving them as part of a page. This lets me use the browser tools (debugger/inspector etc) It also means that the specs are running on the same platform as the code (no bugs that only happen in the specs).

To run these in CI, I wrote a script using capybara. It visits the URL for each of the spec files and scrapes the pages to determine success/failure. However, it was slow - the suite for our app took over 100 seconds.

So I sat down and hacked together a faster script. Rather than completely replacing my CI script, I just got it running a single test file. This individual specs running about 5 times faster.

Then I realised that without the overhead of loading a firefox instance, there was no reason not to run all the specs in parallel. Some quick shell scripting and I was there:

find public/spec/integration -iname *.js | grep -v _spec_helper.js | sed s/^public.spec.//g | xargs -L1 -P30 ./lib/tasks/

Hey presto! the entire suite ran in under 7 seconds, even on my ancient, groaning hardware.

Next, I set up a textmate bundle so I could hit command-R to launch the spec in a browser, and command-D to run it using phantom. Then, I set up a Guardfile

Now I’m wondering if I could fork from within PhantomJS to speed things up further - but that’s a post for another day.

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