I'm currently using CakePHP 2.1.1 with PHP 5.3 and want to upgrade to PHP 5.5 (integrated OPCache), though I'm not sure if CakePHP is compatible with it. Is there an easy way to figure out if those two versions are compatible without installing it beforehand?
Maybe some hint in the documentation?
First of all, you should really, really upgrade your CakePHP installation, 2.1.1 is already 3+ years old.
That being said, you can always check the Travis CI configuration and results for a specific branch/version to figure which PHP versions are compatible. The first CakePHP version being tested against PHP 5.5 out of the box is version 2.3.6
In case the desired PHP version isn't being tested already, you can always fork the CakePHP GitHub repo and add additional PHP Versions to the Travis CI configuration to see whether the tests are passing (requires a Travis CI account and a GitHub Hook).