tests: fix environment not being replaced soon enough

tests/modmail/conftest.py

@@ -6,6 +6,9 @@
 import pytest
 
 
+_ORIG_ENVIRON = None
+
+
 def pytest_report_header(config) -> str:
     """Pytest headers."""
     return "package: modmail"
@@ -24,16 +27,16 @@ def _get_env():
 
 
 def pytest_configure():
-    """Check that the test specific env file exists, and cancel the run if it does not exist."""
+    """Load the test specific environment file, exit if it does not exist."""
     env = _get_env()
     if not env.is_file():
         pytest.exit(f"Testing specific {env} does not exist. Cancelling test run.", 2)
+    os.environ.clear()
+    dotenv.load_dotenv(_get_env(), override=True)
 
 
-@pytest.fixture(autouse=True, scope="package")
-def standardize_environment():
-    """Clear environment variables except for the test.env file."""
-    env = _get_env()
-    with unittest.mock.patch.dict(os.environ, clear=True):
-        dotenv.load_dotenv(env)
-        yield
+def pytest_unconfigure():
+    """Reset os.environ to the original environment before the run."""
+    if _ORIG_ENVIRON is not None:
+        os.environ.clear()
+        os.environ.update(**_ORIG_ENVIRON)