Djblets ships with a custom MySQL backend, which is designed to address

some limitations in older versions of Django. It inherits from the

Django MySQL backend, which will raise an ImproperlyConfigured when

the mysqlclient dependency is missing. Unfortunately, since this is no

longer a development requirement for Djblets, it means we end up with

one general error (not tied to a test) during test discovery.
While raising ImproperlyConfigured is more correct, we're addressing

this by always allowing the module to import and to just inherit from

object if the parent class cannot be loaded. This fixes unit tests,

and if the dependency is missing in production, the backend will really

just flat-out break.

Unit tests pass with and without mysqlclient installed.