Tests in the 'common', 'corpus', 'lib', and 'mapping' folders and the
top-level 'corpus' directory are copied verbatim from the BSON distribution
on CPAN.  Because they invoke BSON.pm for encoding and decoding, they will
pick up BSON::XS and use it for tests.

The t/pvtlib/CleanEnv.pm module in the *BSON* distribution blocks BSON::XS.
The t/pvtlib/CleanEnv.pm module in *this* distribution blocks BSON::PP.  This
way, we can use the same set of tests for both distributions, ensuring
backend compatibility.

See the devel/sync-bson-tests.pl file to automatically update files from
the BSON distribution.
