Python extension testing: Access and manipulate stage for testing

I am writing tests for a python Omniverse (Isaac Sim) extension. The extension converts data from the scene, e.g. positions of objects, to a different data format. Therefore, I would like to programmatically create a scene in the test class and then call the function from the extension.

The function in the extension accesses the prims in the current stage with the get_prim_at_path() function from omni.isaac.core.utils.prims. So I tried to create a test prim in the test function with the create_prim() function from that module. But it seems, that the extension and the test class have different stages, as the extension does not recognize the created prim.

How can I access and manipulate the current stage of the extension within my test class?