You warrant you wrote the code yourself, then it is found your code infringes on code owned by other entities. Now you have a tough choice: admit you lied about writing your code yourself tainting all of the code you claim you wrote since these tools became available or stand and take the infringement penalty which could be very substantial.

Judges and courts don't like playing silly games like this.

I've sued two parties for copyright infringement and won and a third settled out of court for a substantial sum. You don't tell a judge you don't need to prove you wrote the code, that's an automatic loss. Then there are such things as expert witnesses who will interview you and check how much you know about the code you claim you wrote.