Why are some Django methods PascalCase and others snake_case?

As far as I know, the convention is to use snake_case for method names, so why are some methods in Django PascalCase, e.g. Django's TestCase Class?

Django's Testing framework inherits from Python's unittest module. That, in turn, is heavily based on the Java JUnit framework. Java uses PascalCase naming conventions; when the code was ported to Python the names were kept.