Something prevents me from reaching no space left on iPod I want to reach the disk space limit of my iPod touch to handle the 'no space left' condition in my app. In order to do that, I've been sending big files to fill the space of the disk.

I send the files with iTunes, but somehow the memory limit is never reached. It seems that everytime I try to reach the limit with these transfers, iTunes is automatically copying older files from my ipod to my macbook in order to create space for the new files. At least it seems so, but I'm not sure. Something else could be happening but I don't know what.

My iPod touch is on iOS 9.3.5 and I have the latest macbook pro.
I don't know if this was available on iOS 9.5 but on iOS 11 there is an option to conserve space on ios devices. What this does is remove apps that you haven't used to make rooom for new apps or files. I suppose it only removes Apple Store apps since you can easily restore those. this sure sounds like what your iPod may be doing. On my iphone this is turned on by going to Settings/General/iPhone Storge. There is an option there to turn it on. To turn it off go to 'iTunes and App Store' and scroll down to Offload Unused Apps and turn it off there.