Revert "Revert testing changes"

This reverts commit b512ca5.

Author: carlcsaposs-canonical

tox.ini

@@ -41,7 +41,7 @@ description = Run unit tests
 commands_pre =
     poetry install --only main,charm-libs,unit
 commands =
-    poetry run pytest --numprocesses 120 --cov=src --ignore={[vars]tests_path}/integration/ {posargs}
+    poetry run pytest --cov=src --ignore={[vars]tests_path}/integration/ {posargs}
 
 [testenv:integration]
 description = Run integration tests