Last time I checked, the DBD::DB2 tests were superficial and didn't do anything whatsoever with DB2 (past loading the libraries). Which is why DB2::db's tests actually connect to a server, create a database, and do some minor stuff with it.

That said, DBD::DB2 still does need the install path for DB2 (v8.2 by the sounds of the OP's question) to compile/link. I've been after the author of DBD::DB2 for years to get better tests into the suite, but he does this on company time (IBM actually pays someone to develop this), and this is but one of his responsibilities.