Instead of text_data use key_data property to check for uniqueness.
Brown paper bag fix, querying for TextProperty is not smart ^_^.
Patch by: Lennard de Rijk, Sverre Rabbelier
Reviewed by: to-be-reviewed
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html