Check for django-polymorphic-tree install state

It needs to be installed so that the admin templates are loaded.

Author: meshy

conman/routes/apps.py

@@ -11,4 +11,5 @@ class RouteConfig(AppConfig):
     def ready(self):
         """Register checks for conman routes."""
         register(checks.polymorphic_installed)
+        register(checks.polymorphic_tree_installed)
         register(checks.subclasses_available)

conman/routes/checks.py

@@ -18,6 +18,22 @@ def polymorphic_installed(app_configs, **kwargs):
     return errors
 
 
+def polymorphic_tree_installed(app_configs, **kwargs):
+    """Check that Django Polymorphic Tree is installed correctly."""
+    errors = []
+    try:
+        apps.get_app_config('polymorphic_tree')
+    except LookupError:
+        error = Error(
+            'Django Polymorpic Tree must be in INSTALLED_APPS.',
+            hint="Add 'polymorphic_tree' to INSTALLED_APPS.",
+            id='conman.routes.E003',
+        )
+        errors.append(error)
+
+    return errors
+
+
 def subclasses_available(app_configs, **kwargs):
     """Check that at least one Route subclass is available."""
     errors = []

conman/routes/tests/test_checks.py

@@ -36,6 +36,35 @@ def test_not_installed(self):
         self.assertEqual(errors, [error])
 
 
+class TestPolymorphicTreeInstalled(SimpleTestCase):
+    """Test checks.polymorphic_tree_installed."""
+    check = staticmethod(checks.polymorphic_tree_installed)
+
+    def test_registered(self):
+        """checks.polymorphic_tree_installed is a registered check."""
+        registered_checks = registry.get_checks()
+        self.assertIn(self.check, registered_checks)
+
+    def test_installed(self):
+        """The check passes if django-polymorphic-tree is installed."""
+        with self.settings(INSTALLED_APPS=['conman.routes', 'polymorphic_tree']):
+            errors = self.check(app_configs=None)
+
+        self.assertEqual(errors, [])
+
+    def test_not_installed(self):
+        """The check fails if django polymorphic is not installed."""
+        with self.settings(INSTALLED_APPS=['conman.routes']):
+            errors = self.check(app_configs=None)
+
+        error = Error(
+            'Django Polymorpic Tree must be in INSTALLED_APPS.',
+            hint="Add 'polymorphic_tree' to INSTALLED_APPS.",
+            id='conman.routes.E003',
+        )
+        self.assertEqual(errors, [error])
+
+
 class TestSubclassesAvailable(SimpleTestCase):
     """Test checks.subclasses_available."""
     def test_registered(self):