Yes, they're both useful. Runtime logs tell what the program does, source code tells what it thinks it's doing and what the expected answer is.
Testing with a custom exe that loads krmovie.dll reveals that Kirikiri can run ChangeD3DDevice properly on the testbot, so clearly this test needs to be fixed somehow. Is there a button to mark a MR as draft while I figure out exactly how, other than closing it and opening a new one?