You may find that just searching SO for SDP will yield you enough SDP's for you to utilize in your tests... I know I did a quick search and I was surprised at the number!
Another thing to keep in mind is that various attributes can be registered with IANA at any time...
https://www.rfc-editor.org/rfc/rfc4566 - 8.2.4. Attribute Names ("att-field")
Attribute field names ("att-field") MUST be registered with IANA and
documented, because of noticeable issues due to conflicting
attributes under the same name. Unknown attributes in SDP are simply
ignored, but conflicting ones that fragment the protocol are a
serious problem.
There are also other items in the SDP which can change if they are registered with IANA.
You will want to check their site http://www.iana.org/protocols/
Specifically http://www.iana.org/assignments/sdp-parameters/sdp-parameters.xml but most likely others.
You could also then make a program to download each xml file and create a random SDP based on the information from the xml files and then test parsing it but since you made the files that wouldn't be much of a test...