I'm proud of this new config option I added to CPAN.pm: trust_test_report_history.
When this option is set and the latest version of CPAN::Reporter is installed, then CPAN.pm won't run tests on a distribution that has already passed tests on that platform and perl, but will use the last test result for that distribution instead.
Where this comes in handy is "build_requires" prerequisites. If a build_requires prereq is not installed, CPAN.pm will download, build and test it and then include it in PERL5LIB (if it passes its tests) for the rest of that session. But in any future session, the next time a distribution has that prerequisite, CPAN.pm does the exact same thing all over again. But with "trust_test_report_history", the test is only run once.
This may not have a big impact for day-to-day use, but it should save a lot of time and processor cycles for smoke testing.