Interesting lesson? Last August, a contributor wanted to fix something in #django-money's contrib.django_rest_framework. The PR had no tests, a few people mentioned that they'd like to have it merged.
So 9 months later, a maintainer (eh me), gives up and helps to write a few tests and get this thing merged. But no one with acclaimed DRF skillz had reviewed it.
Afterwards, it broke DRF integration in two ways: Two great new contributors came by, fixed it w/ tests!
