How to run django test on google cloud platform

i'm deploying my app on Google Cloud platform. Every thing seems to be set up correctly but when i try to launch test, i get this error :

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ERROR: purbeurre.core (unittest.loader._FailedTest)
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ImportError: Failed to import test module: purbeurre.core
Traceback (most recent call last):
  File "/usr/lib/python3.6/unittest/loader.py", line 462, in _find_test_path
    package = self._get_module_from_name(name)
  File "/usr/lib/python3.6/unittest/loader.py", line 369, in _get_module_from_name
    __import__(name)
ModuleNotFoundError: No module named 'purbeurre.core'

Is there a special setting to have all my test modules loaded ?

i did check locally and it's working on my dev environnement