Self-contained instant functional test suites

I first learned about functional test suites when I started working on the My Opera code. Two years and some time later, I found myself slightly hating the My Opera functional test suite.

The main reasons:

  • It's too slow. Currently, it takes anywhere between 20 and 30 minutes to complete. Sure, it's thousands of tests, divided into hundreds of test scripts, grouped by functional area, like login, blogs, albums, etc…

    Even considered all of this, I think we should aim to have a single functional test run complete in 5-10 minutes.

    Most of the time is being wasted in the communication with the test server and creation and destruction of the database.

  • It's unreliable, sometimes cumbersome to manage. In our setup, CruiseControl fires a functional test suite run after every commit into the source code repository.

    That initiates an ssh connection to the test server, where a shell script takes care of restarting the running apache, dropping and creating the test database, updating required packages, etc…

    This implies that you need an apache instance running on a specific port, a mysql instance running on another port, etc… In the long run, this proved to be an approach that doesn't scale very well. It's too error prone, and not very reliable. Maybe your test run will fail because mysql has mysteriously crashed, or some other random bad thing.

A functional test suite that sucks less

Given the motivation, I came up with this idea of a functional test suite that is:

  1. instant: check out the source code from the repository, and you're ready to go.
  2. self-contained: it shouldn't have any external servers that need to be managed or even running.
  3. reusable: it doesn't have to be a functional test suite. The same concept can be reused for unit test suites, or anything really.

A few months later the first idea, and a couple of weeks of work on it, and we were ready with the first prototype. Here's how we use it:

  • Check out the source code from the repository in ~/src/myproject
  • cd ~/src/myproject
  • ./bin/run-functional-test-suite
  • Private instances of Apache, MySQL, and the main application are created and started
  • A custom WWW::Mechanizer-based client runs the functional test cases against the Apache instance
  • A TAP stream from the test run is produced and collected
  • All custom instances are destroyed
  • ???
  • Profit!

The temporary test run directory is left there untouched, so you can inspect it in case of problems. This is priceless, because that folder contains all the configuration and log files that the test run generated.

The main ideas

  • The entire functional test suite should run within a unique temporary directory created on the fly. You can run many instances as you want, with your username or a different one. They won't conflict with each other.
  • Use as much as possible the same configuration files as the other environments. If you already have development, staging and production, then functional-test is just another one of your environments. If possible, avoid creating special config files just for the functional test suite.
  • The Apache, MySQL, and Application configuration files are simple templates where you need to fill in the apache hostname, apache port, mysql port, username, password, etc…
  • Apache is started up from the temporary directory using the full command invocation, as:

    /usr/sbin/apache2 -k start -f /tmp/{project}_{user}_testsuite_{pid}/conf/apache.conf

    and all paths in config files are absolute, to avoid any relative references that would lead to files not found.
    The configuration template files have to take this into account, and put a $prefix style variable
    everywhere, like (Apache config, for example):

    Timeout 10
    Keepalive On
    HostnameLookups Off
    Listen [% suite.apache.port %]

  • The MySQL instances are created and destroyed from scratch for every test suite run, using the amazing MySQL::Sandbox. My colleague Terje had to patch the sandbox creation script to fix a problem with 64-bit environments. We filed a bug on the MySQL::Sandbox RT queue about this. This is the only small problem found in a really excellent Perl tool. If you haven't looked at it, do it now.

All in all, I'm really satisfied of the result. We applied it to the Auth project for now, which is smaller than My Opera, and we fine-tuned the wrapping shell script to compensate for the underlyiung distribution automatically. We've been able to run this functional test suite on Ubuntu from version 8.04 to 10.04, and on Debian Lenny, with no modifications. The required MySQL version is detected according to your system, and MySQL::Sandbox is instructed accordingly.

It also results in a faster execution of the entire functional test suite.

What can we improve?

There's lots of things to improve:

  • Speed. Instead of creating and destroying the database for every test group, it would be nice to use transactions, and rollback everything at the end of the test group (t/{group-name}/*.t). I used to do this many years ago with Postgres, and it was perfectly safe. I'm not sure we will ever make it with MySQL, since for example, ALTER TABLE (and other SQL statements) completely ignores transactions.
  • Reliability. The private instances of Apache, MySQL (and recently we added memcached too), are started up from ports that are calculated from the originating bash script PID. So, if you run the test suite from the bash script running as PID 8029, then MySQL is started up on port 8030, Apache on 8031, memcached on 8032. This has worked very well for now, and we made sure we don't use ports < 1024, but could lead to mysterious failures if some local services are using ports like 5432, or others. The idea is that we could test if a port is available before using it. However, this error is already detected at startup time, so it shouldn't be a huge problem.

Feedback welcome!

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