[TYPO3-core] FYI24: #14655: Caching framework: Implement PDO backend

[Christian Kuhn]

Hey,

Oliver Klee wrote:
> Thanks for caring about the tests!

Did I ever tell that I *love* unit tests?

For the PDO backend I did the following:
1. Do initial sync of the implementation, uncomment nearly all code to 
stubs methods, fix all fatals
2. Revive / rewrite the first simple test and fix the implementation, 
get green bar feeling
3. Revive the next test, fix code, and so on, until all test are fine
4. Add further tests which are missing / not needed in FLOW3
5. Have a running implementation and finally test it in real life 
(worked immediately).

Without all those tests for the caching framework, the sync from FLOW3 
would have been nearly impossible and error prone. And I learned a lot. 
Take a look at the (soon committed) file backend tests, Karsten & Robert 
did some nifty mocking for some cases.

I think it would be great if we could dedicate a bugday to unit tests in 
the future. There are some classes, like t3lib_div, where unit tests are 
easy to hack up (no dependencies) and would help a lot.

Regards
Christian