We know that the conformance test for MPEG audio is defined in part-4 of the ISO standard.
There are bitstreams for the conformance (compliance) testing for different MPEG audio decoders, MP3, AAC for example.
But the file size of these bitstreams are smaller than the others algorithms, like WMA, AC-3 and DTS.

1. These MPEG bitstream can guarantee that if any decoder passes these compliance tests, that decoder would be good enough to decode the other bitstreams?

2. Why the other algorithms, WMA, AC-3, DTS need more bitstreams for doing that? And the file size of them seem bigger than ISO's.

Any comment is appreciated.

In the mp3 case, the compliance bitstreams are not enough. Decoders can pass them but still encounter problems on some real-life bitstreams.

And how to check if a given bitstream is compliant to standard? Is there any public-available checkers or something?

There is no way to check unless using interoperability tests.
Unfortunately when the mp3 standard was defined, interoperability tests were not yet something usual.

So That is the reason why in WMA, AC-3 and DTS cases, which include many many compliance bitstreams to ensure that the above decoders could be robust to decode the real-life bitstream?

Why doesn't MPEG support bitstreams enough to make sure the certification of the MPEG decoder?
I think this is very important for the applications that used MPEG decoder.
It seems that AC-3 and DTS do a good job in that.