A test that asserts what the decoder currently does proves nothing. Every
legal frame here is compared byte for byte with what pyzstd decompressed it
to, and every malformed frame is one pyzstd also refuses.
The refusal has to be a ZstdException. RangeError, OutOfMemoryError and
IndexError are all Error rather than Exception, so a caller writing
"on ZstdException" does not catch them and the isolate dies.
