Change way we patch test

Author: seddonym

tests/functional/test_build_and_use_graph.py

@@ -3,7 +3,7 @@
 import pytest
 from unittest.mock import patch
 from grimp.application import usecases
-import os
+
 
 """
 For ease of reference, these are the imports of all the files:
@@ -56,9 +56,7 @@ def test_modules():
     }
 
 
-@patch.object(
-    os, "environ", {usecases.MIN_NUMBER_OF_MODULES_TO_SCAN_USING_MULTIPROCESSING_ENV_NAME: "0"}
-)
+@patch.object(usecases, "DEFAULT_MIN_NUMBER_OF_MODULES_TO_SCAN_USING_MULTIPROCESSING", 0)
 def test_modules_multiprocessing():
     """
     This test runs relatively slowly, but it's important we cover the multiprocessing code.