Move logic to determine IS_RUNNING_TESTS to a function

This makes the logic testable.

debug_toolbar/settings.py

@@ -7,6 +7,15 @@
 from django.dispatch import receiver
 from django.test.signals import setting_changed
 
+
+def _is_running_tests():
+    """
+    Helper function to support testing default value for
+    IS_RUNNING_TESTS
+    """
+    return "test" in sys.argv or "PYTEST_VERSION" in os.environ
+
+
 CONFIG_DEFAULTS = {
     # Toolbar options
     "DISABLE_PANELS": {
@@ -44,7 +53,7 @@
     "SQL_WARNING_THRESHOLD": 500,  # milliseconds
     "OBSERVE_REQUEST_CALLBACK": "debug_toolbar.toolbar.observe_request",
     "TOOLBAR_LANGUAGE": None,
-    "IS_RUNNING_TESTS": "test" in sys.argv or "PYTEST_VERSION" in os.environ,
+    "IS_RUNNING_TESTS": _is_running_tests(),
     "UPDATE_ON_FETCH": False,
 }
 

tests/test_settings.py

@@ -0,0 +1,22 @@
+from unittest.mock import patch
+
+from django.test import TestCase
+
+from debug_toolbar.settings import _is_running_tests
+
+
+class SettingsTestCase(TestCase):
+    @patch("debug_toolbar.settings.sys")
+    @patch("debug_toolbar.settings.os")
+    def test_is_running_tests(self, mock_os, mock_sys):
+        mock_sys.argv = "test"
+        mock_os.environ = {}
+        self.assertTrue(_is_running_tests())
+
+        mock_sys.argv = ""
+        mock_os.environ = {}
+        self.assertFalse(_is_running_tests())
+
+        mock_sys.argv = ""
+        mock_os.environ = {"PYTEST_VERSION": "1"}
+        self.assertTrue(_is_running_tests())