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A lot of core files will be patched (~76 CE, ~85 EE). If I take a look at the files I do see a lot of different modules are affected: PayPal, Newsletter, Import/Export, Authorize, Checkout, ...
I can apply the patch successfully on a dev site. But how can I check if it doesn't break anything? Placing an order works - but does it make sense to test all related modules? Or is it safe to push it live?