title: Sharing unit testing fixtures
body: <p>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).</p>
  
  <p>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 <code>setUpBeforeClass()</code> and static properties).</p>
  
  <p>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.</p>
  
  <p>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".</p>
  
  <p>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?</p>