This PR adds a missing test for the -maxtipage parameter which controls what is the allowed maximum tip age for leaving IBD:
https://github.com/bitcoin/bitcoin/blob/792d0d8d512cf8ddca200317b74ce550c1a1a428/src/init.cpp#L540
Relevant code path in the CChainState::IsInitialBlockDownload method:
https://github.com/bitcoin/bitcoin/blob/792d0d8d512cf8ddca200317b74ce550c1a1a428/src/validation.cpp#L1479-L1480
The test is pretty simple and should be self-explanatory.