I think `GraphiteMetric.from_config()` should be a separate thing that needs to be tested. Throughout diamondash, the `SomeClass.from_config()` relies on `SomeClass.parse_config()`, and since `from_config()` is the same for every class (since it is inhereted from `ConfigMixin`, testing `from_config()` is basically testing `parse_config()`. If I should test `GraphiteMetric.parse_config()` in `GraphiteBackend.parse_config()`, then I should also be testing `GraphiteBackend.parse_config()` (along with `GraphiteMetric.parse_config()`) in `GraphWidget.parse_config()` and in `LValueWidget.parse_config()`. Similarly, I would need to test each widget type's `parse_config()` in `Dashboard.parse_config()`.

It starts getting very complicated if I don't mock things that way. Can we not just expect `from_config()` to do what we are expected it to do in each case (return an instance constructed from a config) and mock it out?