Assuming you're using the PLCrashReport API to actually parse the protobuf report, this is a bit more tricky than it needs to be, mainly because the API necessary to create arbitrary PLCrashReport instances — the only option is to parse an actual report.
Your best bet would be to generate a crash report (eg, via -[PLCrashReporter generateLiveReport]), use it as a static test resource, and write your tests against that known data.
This is a use case we should support better, though, so I've filed a PLCrashReporter issue to track the request.