Sharing unit testing fixtures

Question

I'm writing unit tests for a project (written in PHP, using PHPUnit) that have its entire environment (loaded components, events, configuration, cache, per-environment singletons, etc) held in an object which all the components use to interact with each other (using a mediator pattern).

In order to make the unit tests run faster, I'm sharing the environment object and some other objects (for example, in my test case for view object [as in the V of MVC], the view manager object [which acts as a factory for view objects and responsible for the actual rendering]) among tests in the same test case (using PHPUnit's setUpBeforeClass() and static properties).

Even though, to the best of my knowledge, the objects I share shouldn't effect the integrity of the tests (in the views case, for example, the environment and view manager object are shared, but a separate view object is created for every test - which is the object that's actually being tested by the test case), it just feels increasingly wrong to me.

I would prefer it if each test used a completely isolated environment and couldn't effect other tests in the same test case in any way. However, that would make the tests run much slower and it feels like a big price for something that I can't really pinpoint the downside of and mainly just "feels wrong".

What do you think? Can you pinpoint any downsides so I can convince myself its worth the longer execution time? Or am I just over reacting and its completely fine?

Answer 1

I share your feelings so maybe i just state my goals and my solution when i faced that issue:

• Devs should have a test suite that runs very very fast
• At least single test cases should execute in less than a second
• I really want to be sure i don't have interdependencies in my test cases

I'm going to assume you have a Continuous Integration Server running. If not a cronjob might do but consider setting up jenkins, it's really really easy.

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For normal usage:

Just share as much fixtures as you need to get the speed you need. It might not be pretty and there might be better solutions along the way but if you have something that is expensive to create just do it once.

I'd suggest helper methods getFoo() { if(!self::$foo) .... create ... return $foo;} over setUpBeforeClass because it can make sharing easier but mainly because of the following point.

Once a night:

Run your test suite with --process-isolation and in that bootstrap recreate your complete database and everything.

It might run 6 hours (disable code coverage for that!) but how cares. Your fixtures will be recreated for every single test case since it's a new php process and the static vars don't exist.

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Using this way you can be sure that you don't have created dependent once a day. Thats good enough to remember what you did (and you can run with --filter and --process-isolation if you need to fix something).