How to define variable in class out of class and use it in IF statement

Everyone hello. I have learning Python for 2 months, and now I am learning OOP. And I have a question:

class Test():
x = 0

def __init__(self):

    if Test.x == 5:
        print("OK")
    else:
        print("ERROR")
        
i = Test()
i.x = 5

And this is output:

ERROR

Why this code returns me an "ERROR", if x = 5? In my opinion it may return me an "OK"