Its what I just paid on a testnet transaction using the core devleopers android app, I made nothing up, just used the recommended fee. Yes the fee can be less, but realistically a low or zero fee transaction is unlikely to be included in a block if the network is busy.
Testnet transactions are irrelevant, testnet like its name suggest is meant for testing. Recommended fees are also irrelevant, because most/all wallets are notoriously bad at "recommending" fees. If you want to know the real fees, look at sites like
https://jochen-hoenicke.de/queue/#0,24h , they show the current stats. At this moment, even 1 satoshi/byte fees are easily getting included in blocks. For now on-chain Bitcoin transactions are very cheap.
Also, there's no such thing as "core developer's android app".