$ prove db.t
db....Name "Test::MockDBI::errstr" used only once: possible typo at db.t line 24.
db....ok 2/4errstr:DBI error at 'select i from t' at db.pm line 32.
# Looks like you planned 4 tests but only ran 2.
# Looks like your test died just after 2.
db....dubious
        Test returned status 255 (wstat 65280, 0xff00)
DIED. FAILED tests 3-4
        Failed 2/4 tests, 50.00% okay
Failed Test Stat Wstat Total Fail  Failed  List of Failed
-------------------------------------------------------------------------------
db.t         255 65280     4    4 100.00%  3-4
Failed 1/1 test scripts, 0.00% okay. 2/4 subtests failed, 50.00% okay.