Clear Test App Cache Prior to TestSuite

[mostertb]

The cache of the bundled Symfony Application is not cleared in between executions of the PHPUnit test suite. This sometimes causes false positives on test failures (particularly when modifying code that affects Dependency Injection).

Clearing and warming up the Symfony cache is, however, very slow so we should avoid doing this is a setUp() or setUpBeforeClass(). The best option would be if it could be done once per execution of the phpunit.

A potential solution could be to define our own autoloading file that first calls the composer autoloader and then does the cache clear. A console entrypoint has already been added to help with this

[pierredup]

What do you think about using a virtual file system for the cache?

Using something like vfsStream will give the benefit that you never have to worry about clearing cache, dangling cache files on the file system or even file permissions (if something is not configured properly)
.
The down side is that the cache is rebuilt on each run, which does have a performance impact, but for me the test suite executes in less than 6 seconds, so the performance hit is not that bad currently. But it can potentially become worse with each new test added.

I have added a commit for this (a relatively small change) which you can look at. If you are interested in using this approach, then I can create a PR.