Fix #50 -- Add check for placeholders missing URL config

Author: codingjoe

pictures/apps.py

@@ -0,0 +1,8 @@
+from django.apps import AppConfig
+
+
+class PicturesAppConfig(AppConfig):
+    name = "pictures"
+
+    def ready(self):
+        import pictures.checks  # noqa

pictures/checks.py

@@ -0,0 +1,34 @@
+from django.core.checks import Error, Tags, register
+from django.urls import NoReverseMatch, reverse
+
+from . import conf
+
+__all__ = ["placeholder_url_check"]
+
+
+@register(Tags.urls)
+def placeholder_url_check(app_configs, **kwargs):
+    errors = []
+    if conf.get_settings().USE_PLACEHOLDERS:
+        try:
+            reverse(
+                "pictures:placeholder",
+                kwargs={
+                    "alt": "test",
+                    "width": 100,
+                    "ratio": "1x1",
+                    "file_type": "jpg",
+                },
+            )
+        except NoReverseMatch:
+            errors.append(
+                Error(
+                    "Placeholder URLs are not configured correctly.",
+                    hint=(
+                        'PICTURES["USE_PLACEHOLDERS"] is True,'
+                        ' but include("pictures.urls") is missing for your URL config.'
+                    ),
+                    id="pictures.E001",
+                )
+            )
+    return errors

tests/test_checks.py

@@ -0,0 +1,20 @@
+from unittest.mock import Mock
+
+from django.urls import NoReverseMatch
+
+from pictures import checks
+
+
+def test_placeholder_url_check(settings, monkeypatch):
+    """Test that the placeholder URL check works."""
+
+    settings.PICTURES["USE_PLACEHOLDERS"] = True
+    assert not checks.placeholder_url_check({})
+
+    reverse = Mock(side_effect=NoReverseMatch)
+    monkeypatch.setattr(checks, "reverse", reverse)
+
+    assert checks.placeholder_url_check({})
+
+    settings.PICTURES["USE_PLACEHOLDERS"] = False
+    assert not checks.placeholder_url_check({})