This would only work if we would instantiate the TestRun class so the get_test_folder() method will be bound.
If we just try to remove the self argument here we fail with 
```
TypeError: unbound method get_tests_folder() must be called with TestRun instance as first argument (got nothing instead)
```

To make this consistent we should instantiate the TestRun class for each testrun type and use the newly bound object to call all the methods.