Saying Shahadah would be necessary in the case that want to choose your religion as Islam. Of course you say Shahada in your Salahs everyday, namely:

> اَشْهَدُ اَنْ لااِلهَ اِلاّ اللهُ وَحْدَهُ لاشَريكَ لَهُ وَ اَشْهَدُ
> اَنَّ مُحَمّداً عَبْدُهُ وَ رَسولُهُ.

**But if you really did a Kufr as an practice which made you as a Kafir, then you ought to say Shahadah as well.**

In truth, doing that (Kufr) knowingly or unknowingly would be so significant in the result of that. Actually it doesn't seem to be necessary in the case of Unknowing ... / But in the case of knowingly seems to be necessary for you to ... Since in fact you have leave Islam, then you ought to enter it again!

And Allah knows best