Questions about padding oracle attacks

I’m working my way through a challenge (which I will not name due to spoilers) and I’ve been learning about padding oracle attacks. I’ve got some questions about them.

  1. How would one know if a site is susceptible to a padding oracle attack?
  2. Are there some tests that can be run to see if a padding oracle attack may be possible?
  3. How would one find the block size that a site uses for a padding oracle attack?

Thanks

1 - https://www.owasp.org/index.php/Special:Search/Testing_for_Padding_Oracle ( Look down into the contects for the links )

And how to perform it : http://www.hackingarticles.in/hack-padding-oracle-lab/

U can try firstly “Padding Oracle” iso from pentesterlab site.