default* (and I think these would be better as inline comments -- the `msg` kwarg kinda clutters things IMO and probably doesn't offer much benefit)
also, I would chop the intermediate variables and just multiline the assertEqual if you think the line is too long (although the 80 character limit is a soft limit in code)
```
assertEqual(
    list(iter_format_modules('de')),
    [default_mod])
)
```
"One big exception to PEP 8 is our preference of longer line lengths. We’re well into the 21st Century, and we have high-resolution computer screens that can fit way more than 79 characters on a screen. Don’t limit lines of code to 79 characters if it means the code looks significantly uglier or is harder to read." https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/coding-style/