Why can test private methods/fields in Spock without problems?

Question

package com.example.dev;
public class AClass {
 private Integer a =10;
...//other code
}

and when I try to access a in my Spock method:

Answer 1

Spock isn't guilty, it's groovy itself, see: Private method in groovy is not private.

While it's possible to refer to private members of class, it's definitely not a good practice.