Improve get_app_conf robustness and add skip_missing_app parameter support

- Added new optional parameter 'skip_missing_app' to get_app_conf() in module_utils/config_utils.py to safely return defaults when applications are missing.
- Updated group_vars/all/00_general.yml and roles/web-app-nextcloud/config/main.yml to include skip_missing_app=True in all Nextcloud-related calls.
- Added comprehensive unit tests under tests/unit/module_utils/test_config_utils.py covering missing app handling, schema enforcement, nested lists, and index edge cases.

Ref: https://chatgpt.com/share/68ee6b5c-6db0-800f-bc20-d51470d7b39f

tests/unit/module_utils/test_config_utils.py

@@ -0,0 +1,125 @@
+import os
+import shutil
+import tempfile
+import unittest
+
+from module_utils.config_utils import (
+    get_app_conf,
+    AppConfigKeyError,
+    ConfigEntryNotSetError,
+)
+
+class TestGetAppConf(unittest.TestCase):
+    def setUp(self):
+        # Isolate working directory so that schema files can be discovered
+        self._cwd = os.getcwd()
+        self.tmpdir = tempfile.mkdtemp(prefix="cfgutilstest_")
+        os.chdir(self.tmpdir)
+
+        # Minimal schema structure:
+        # roles/web-app-demo/schema/main.yml
+        os.makedirs(os.path.join("roles", "web-app-demo", "schema"), exist_ok=True)
+        with open(os.path.join("roles", "web-app-demo", "schema", "main.yml"), "w") as f:
+            f.write(
+                # Defines 'features.defined_but_unset' in schema (without a value in applications),
+                # plus 'features.oidc' and 'features.nested.list'
+                "features:\n"
+                "  oidc: {}\n"
+                "  defined_but_unset: {}\n"
+                "  nested:\n"
+                "    list:\n"
+                "      - {}\n"
+            )
+
+        # Example configuration with actual values
+        self.applications = {
+            "web-app-demo": {
+                "features": {
+                    "oidc": True,
+                    "nested": {
+                        "list": ["first", "second"]
+                    }
+                }
+            }
+        }
+
+    def tearDown(self):
+        os.chdir(self._cwd)
+        shutil.rmtree(self.tmpdir, ignore_errors=True)
+
+    # --- Tests ---
+
+    def test_missing_app_with_skip_missing_app_returns_default_true(self):
+        """If app ID is missing and skip_missing_app=True, it should return the default (True)."""
+        apps = {"some-other-app": {}}
+        val = get_app_conf(apps, "web-app-nextcloud", "features.oidc",
+                           strict=True, default=True, skip_missing_app=True)
+        self.assertTrue(val)
+
+    def test_missing_app_with_skip_missing_app_returns_default_false(self):
+        """If app ID is missing and skip_missing_app=True, it should return the default (False)."""
+        apps = {"svc-bkp-rmt-2-loc": {}}
+        val = get_app_conf(apps, "web-app-nextcloud", "features.oidc",
+                           strict=True, default=False, skip_missing_app=True)
+        self.assertFalse(val)
+
+    def test_missing_app_without_skip_missing_app_and_strict_true_raises(self):
+        """Missing app ID without skip_missing_app and strict=True should raise."""
+        apps = {}
+        with self.assertRaises(AppConfigKeyError):
+            get_app_conf(apps, "web-app-nextcloud", "features.oidc",
+                         strict=True, default=True, skip_missing_app=False)
+
+    def test_missing_app_without_skip_missing_app_and_strict_false_raises(self):
+        apps = {}
+        with self.assertRaises(AppConfigKeyError):
+            get_app_conf(apps, "web-app-nextcloud", "features.oidc",
+                        strict=False, default=True, skip_missing_app=False)
+
+    def test_existing_app_returns_expected_value(self):
+        """Existing app and key should return the configured value."""
+        val = get_app_conf(self.applications, "web-app-demo", "features.oidc",
+                           strict=True, default=False, skip_missing_app=False)
+        self.assertTrue(val)
+
+    def test_nested_list_index_access(self):
+        """Accessing list indices should work correctly."""
+        val0 = get_app_conf(self.applications, "web-app-demo", "features.nested.list[0]",
+                            strict=True, default=None, skip_missing_app=False)
+        val1 = get_app_conf(self.applications, "web-app-demo", "features.nested.list[1]",
+                            strict=True, default=None, skip_missing_app=False)
+        self.assertEqual(val0, "first")
+        self.assertEqual(val1, "second")
+
+    def test_schema_defined_but_unset_raises_in_strict_mode(self):
+        """Schema-defined but unset value should raise in strict mode."""
+        with self.assertRaises(ConfigEntryNotSetError):
+            get_app_conf(self.applications, "web-app-demo", "features.defined_but_unset",
+                         strict=True, default=False, skip_missing_app=False)
+
+    def test_schema_defined_but_unset_strict_false_returns_default(self):
+        """Schema-defined but unset value should return default when strict=False."""
+        val = get_app_conf(self.applications, "web-app-demo", "features.defined_but_unset",
+                           strict=False, default=True, skip_missing_app=False)
+        self.assertTrue(val)
+
+    def test_invalid_key_format_raises(self):
+        """Invalid key format in path should raise AppConfigKeyError."""
+        with self.assertRaises(AppConfigKeyError):
+            get_app_conf(self.applications, "web-app-demo", "features.nested.list[not-an-int]",
+                         strict=True, default=None, skip_missing_app=False)
+
+    def test_index_out_of_range_respects_strict(self):
+        """Out-of-range index should respect strict parameter."""
+        # strict=False returns default
+        val = get_app_conf(self.applications, "web-app-demo", "features.nested.list[99]",
+                           strict=False, default="fallback", skip_missing_app=False)
+        self.assertEqual(val, "fallback")
+        # strict=True raises
+        with self.assertRaises(AppConfigKeyError):
+            get_app_conf(self.applications, "web-app-demo", "features.nested.list[99]",
+                         strict=True, default=None, skip_missing_app=False)
+
+
+if __name__ == "__main__":
+    unittest.main()