More testing and a better warning for tags with multiple attributes

Adds filename and line number to the multiple attributes warning and increases code coverage.

Code Coverage Before:

```
Statements   : 97.39% ( 1380/1417 )
Branches     : 95% ( 741/780 )
Functions    : 95.81% ( 160/167 )
Lines        : 97.55% ( 1315/1348 )
```

Code Coverage After:

```
Statements   : 98.23% ( 1390/1415 )
Branches     : 96.53% ( 751/778 )
Functions    : 96.41% ( 161/167 )
Lines        : 98.44% ( 1326/1347 )
```