Based on the answer to Referencing Qt UIs external to plugin with python. I'm trying to utilize the "Layer Properties / Fields / Python Init function" to execute a file (test_file.py) that is located in the folder of the plugin that I'm making.

I've made sure that the path to my plugin folder is in PYTHONPATH via "Settings / Options... / System / Environment" ... and restarted QGIS.

When the layer, for which I'm utilizing Init function, is initialized and a feature is selected test.py is executed. However, I get three consecutive error messages saying:

1) An error occured during execution of following code:
      import test_file
      Traceback (most recent call last):
        File "", line 1, in 
        File "C:/PROGRA~1/QGISVA~1/apps/qgis/./python\qgis\utils.py", line 453, in _import
          mod = _builtin_import(name, globals, locals, fromlist, level)
      ImportError: No module named test_file
      
2) An error occured during execution of following code:
      if hasattr(test_file,'DEBUGMODE') and test_file.DEBUGMODE:    reload(test_file)
      Traceback (most recent call last):
        File "", line 1, in 
      NameError: name 'test_file' is not defined

      
3) An error occured during execution of following code:
      _qgis_feature_form_20140526104937007 = test_file.py(_qgis_featureform_2, _qgis_layer_workgroups20140526104723778, _qgis_feature_20140526104937007)
      Traceback (most recent call last):
        File "", line 1, in 
      NameError: name 'test_file' is not defined

Any suggestions how to fix this?