Increase test coverage

Currently:

```
Name                                    Stmts   Miss  Cover   Missing
---------------------------------------------------------------------
incuna_auth/__init__                        0      0   100%   
incuna_auth/backends                       16     16     0%   1-21
incuna_auth/forms                           6      6     0%   1-8
incuna_auth/middleware/__init__             4      0   100%   
incuna_auth/middleware/basic_auth          28     21    25%   7-13, 17-24, 44-53
incuna_auth/middleware/login_required      28      6    79%   54, 61-67
incuna_auth/models                          0      0   100%   
incuna_auth/urls                           12     12     0%   1-38
---------------------------------------------------------------------
TOTAL                                      94     61    35% 
```

![http://25.media.tumblr.com/cd4c30468eed57922ebcfebe3ac89b87/tumblr_mtrwuvN0bu1rqp2rqo1_500.gif](http://25.media.tumblr.com/cd4c30468eed57922ebcfebe3ac89b87/tumblr_mtrwuvN0bu1rqp2rqo1_500.gif)