Limit the cases for E001 to likely scenarios (#1925)

Only when the user is customizing both the show toolbar callback
setting and the URLs aren't installed will the underlying
NoReverseMatch error occur.

debug_toolbar/apps.py

@@ -5,10 +5,12 @@
 from django.conf import settings
 from django.core.checks import Error, Warning, register
 from django.middleware.gzip import GZipMiddleware
+from django.urls import NoReverseMatch, reverse
 from django.utils.module_loading import import_string
 from django.utils.translation import gettext_lazy as _
 
-from debug_toolbar import settings as dt_settings
+from debug_toolbar import APP_NAME, settings as dt_settings
+from debug_toolbar.settings import CONFIG_DEFAULTS
 
 
 class DebugToolbarConfig(AppConfig):
@@ -213,7 +215,33 @@ def debug_toolbar_installed_when_running_tests_check(app_configs, **kwargs):
     """
     Check that the toolbar is not being used when tests are running
     """
-    if not settings.DEBUG and dt_settings.get_config()["IS_RUNNING_TESTS"]:
+    # Check if show toolbar callback has changed
+    show_toolbar_changed = (
+        dt_settings.get_config()["SHOW_TOOLBAR_CALLBACK"]
+        != CONFIG_DEFAULTS["SHOW_TOOLBAR_CALLBACK"]
+    )
+    try:
+        # Check if the toolbar's urls are installed
+        reverse(f"{APP_NAME}:render_panel")
+        toolbar_urls_installed = True
+    except NoReverseMatch:
+        toolbar_urls_installed = False
+
+    # If the user is using the default SHOW_TOOLBAR_CALLBACK,
+    # then the middleware will respect the change to settings.DEBUG.
+    # However, if the user has changed the callback to:
+    # DEBUG_TOOLBAR_CONFIG = {"SHOW_TOOLBAR_CALLBACK": lambda request: DEBUG}
+    # where DEBUG is not settings.DEBUG, then it won't pick up that Django'
+    # test runner has changed the value for settings.DEBUG, and the middleware
+    # will inject the toolbar, while the URLs aren't configured leading to a
+    # NoReverseMatch error.
+    likely_error_setup = show_toolbar_changed and not toolbar_urls_installed
+
+    if (
+        not settings.DEBUG
+        and dt_settings.get_config()["IS_RUNNING_TESTS"]
+        and likely_error_setup
+    ):
         return [
             Error(
                 "The Django Debug Toolbar can't be used with tests",

docs/changes.rst

@@ -6,6 +6,9 @@ Pending
 
 * Fixed overriding font-family for both light and dark themes.
 * Restored compatibility with ``iptools.IpRangeList``.
+* Limit ``E001`` check to likely error cases when the
+  ``SHOW_TOOLBAR_CALLBACK`` has changed, but the toolbar's URL
+  paths aren't installed.
 
 4.4.2 (2024-05-27)
 ------------------

docs/configuration.rst

@@ -152,6 +152,16 @@ Toolbar options
      implication is that it is possible to execute arbitrary SQL through the
      SQL panel when the ``SECRET_KEY`` value is leaked somehow.
 
+  .. warning::
+
+     Do not use
+     ``DEBUG_TOOLBAR_CONFIG = {"SHOW_TOOLBAR_CALLBACK": lambda request: DEBUG}``
+     in your project's settings.py file. The toolbar expects to use
+     ``django.conf.settings.DEBUG``. Using your project's setting's ``DEBUG``
+     is likely to cause unexpected results when running your tests. This is because
+     Django automatically sets ``settings.DEBUG = False``, but your project's
+     setting's ``DEBUG`` will still be set to ``True``.
+
 .. _OBSERVE_REQUEST_CALLBACK:
 
 * ``OBSERVE_REQUEST_CALLBACK``

tests/test_checks.py

@@ -1,9 +1,9 @@
 from unittest.mock import patch
 
-from django.core.checks import Error, Warning, run_checks
+from django.core.checks import Warning, run_checks
 from django.test import SimpleTestCase, override_settings
+from django.urls import NoReverseMatch
 
-from debug_toolbar import settings as dt_settings
 from debug_toolbar.apps import debug_toolbar_installed_when_running_tests_check
 
 
@@ -239,39 +239,70 @@ def test_check_w007_invalid(self, mocked_guess_type):
             ],
         )
 
-    def test_debug_toolbar_installed_when_running_tests(self):
-        with self.settings(DEBUG=True):
-            # Update the config options because self.settings()
-            # would require redefining DEBUG_TOOLBAR_CONFIG entirely.
-            dt_settings.get_config()["IS_RUNNING_TESTS"] = True
-            errors = debug_toolbar_installed_when_running_tests_check(None)
-            self.assertEqual(len(errors), 0)
-
-            dt_settings.get_config()["IS_RUNNING_TESTS"] = False
-            errors = debug_toolbar_installed_when_running_tests_check(None)
-            self.assertEqual(len(errors), 0)
-        with self.settings(DEBUG=False):
-            dt_settings.get_config()["IS_RUNNING_TESTS"] = False
-            errors = debug_toolbar_installed_when_running_tests_check(None)
-            self.assertEqual(len(errors), 0)
+    @patch("debug_toolbar.apps.reverse")
+    def test_debug_toolbar_installed_when_running_tests(self, reverse):
+        params = [
+            {
+                "debug": True,
+                "running_tests": True,
+                "show_callback_changed": True,
+                "urls_installed": False,
+                "errors": False,
+            },
+            {
+                "debug": False,
+                "running_tests": False,
+                "show_callback_changed": True,
+                "urls_installed": False,
+                "errors": False,
+            },
+            {
+                "debug": False,
+                "running_tests": True,
+                "show_callback_changed": False,
+                "urls_installed": False,
+                "errors": False,
+            },
+            {
+                "debug": False,
+                "running_tests": True,
+                "show_callback_changed": True,
+                "urls_installed": True,
+                "errors": False,
+            },
+            {
+                "debug": False,
+                "running_tests": True,
+                "show_callback_changed": True,
+                "urls_installed": False,
+                "errors": True,
+            },
+        ]
+        for config in params:
+            with self.subTest(**config):
+                config_setting = {
+                    "RENDER_PANELS": False,
+                    "IS_RUNNING_TESTS": config["running_tests"],
+                    "SHOW_TOOLBAR_CALLBACK": (
+                        (lambda *args: True)
+                        if config["show_callback_changed"]
+                        else "debug_toolbar.middleware.show_toolbar"
+                    ),
+                }
+                if config["urls_installed"]:
+                    reverse.side_effect = lambda *args: None
+                else:
+                    reverse.side_effect = NoReverseMatch()
 
-            dt_settings.get_config()["IS_RUNNING_TESTS"] = True
-            errors = debug_toolbar_installed_when_running_tests_check(None)
-            self.assertEqual(
-                errors,
-                [
-                    Error(
-                        "The Django Debug Toolbar can't be used with tests",
-                        hint="Django changes the DEBUG setting to False when running "
-                        "tests. By default the Django Debug Toolbar is installed because "
-                        "DEBUG is set to True. For most cases, you need to avoid installing "
-                        "the toolbar when running tests. If you feel this check is in error, "
-                        "you can set `DEBUG_TOOLBAR_CONFIG['IS_RUNNING_TESTS'] = False` to "
-                        "bypass this check.",
-                        id="debug_toolbar.E001",
-                    )
-                ],
-            )
+                with self.settings(
+                    DEBUG=config["debug"], DEBUG_TOOLBAR_CONFIG=config_setting
+                ):
+                    errors = debug_toolbar_installed_when_running_tests_check(None)
+                    if config["errors"]:
+                        self.assertEqual(len(errors), 1)
+                        self.assertEqual(errors[0].id, "debug_toolbar.E001")
+                    else:
+                        self.assertEqual(len(errors), 0)
 
     @override_settings(
         DEBUG_TOOLBAR_CONFIG={