test(core): add tests for Configuration and ConfigurationModelABC

- ConfigurationModelABC: defaults, src parsing, PascalCase/snake_case
  key variants, type casting, required fields, readonly enforcement,
  env var override with prefix
- Configuration: set/get by class and string key, auto-instantiation
  of unregistered models, add_json_file loading, optional/missing files

Also documents two additional bugs found:
- cast(True, bool) fails with AttributeError (bool has no .lower())
- add_json_file does not exit on invalid JSON (swallows parse error)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/core/configuration/configuration_test.py

@@ -0,0 +1,107 @@
+import json
+import os
+import pytest
+from cpl.core.configuration.configuration import Configuration
+from cpl.core.configuration.configuration_model_abc import ConfigurationModelABC
+
+
+class AppSettings(ConfigurationModelABC):
+    def __init__(self, src: dict = None):
+        ConfigurationModelABC.__init__(self, src or {})
+        self.option("app_name", str, default="default-app")
+        self.option("version", str, default="0.0.0")
+
+
+class ServerSettings(ConfigurationModelABC):
+    def __init__(self, src: dict = None):
+        ConfigurationModelABC.__init__(self, src or {})
+        self.option("host", str, default="localhost")
+        self.option("port", int, default=8080)
+
+
+@pytest.fixture(autouse=True)
+def clear_config():
+    """Reset Configuration state before each test."""
+    Configuration._config.clear()
+    yield
+    Configuration._config.clear()
+
+
+# --- set / get ---
+
+def test_set_and_get_by_class():
+    settings = AppSettings({"app_name": "TestApp", "version": "1.0.0"})
+    Configuration.set(AppSettings, settings)
+    result = Configuration.get(AppSettings)
+    assert result.app_name == "TestApp"
+    assert result.version == "1.0.0"
+
+
+def test_set_and_get_by_string_key():
+    Configuration.set("my_key", "my_value")
+    assert Configuration.get("my_key") == "my_value"
+
+
+def test_get_missing_returns_default():
+    assert Configuration.get("nonexistent", "fallback") == "fallback"
+
+
+def test_get_missing_returns_none():
+    assert Configuration.get("nonexistent") is None
+
+
+def test_get_model_auto_instantiates():
+    # Getting an unregistered ConfigurationModelABC subclass should auto-create it
+    result = Configuration.get(ServerSettings)
+    assert isinstance(result, ServerSettings)
+    assert result.host == "localhost"
+    assert result.port == 8080
+
+
+def test_overwrite_existing():
+    Configuration.set("key", "first")
+    Configuration.set("key", "second")
+    assert Configuration.get("key") == "second"
+
+
+def test_multiple_models():
+    Configuration.set(AppSettings, AppSettings({"app_name": "App"}))
+    Configuration.set(ServerSettings, ServerSettings({"port": 9000}))
+    assert Configuration.get(AppSettings).app_name == "App"
+    assert Configuration.get(ServerSettings).port == 9000
+
+
+# --- add_json_file ---
+
+def test_add_json_file_loads_model(tmp_path):
+    config_data = {"AppSettings": {"app_name": "FromFile", "version": "2.0.0"}}
+    config_file = tmp_path / "appsettings.json"
+    config_file.write_text(json.dumps(config_data), encoding="utf-8")
+
+    Configuration.add_json_file(str(config_file), output=False)
+
+    result = Configuration.get(AppSettings)
+    assert result.app_name == "FromFile"
+    assert result.version == "2.0.0"
+
+
+def test_add_json_file_not_found_exits(tmp_path):
+    with pytest.raises(SystemExit):
+        Configuration.add_json_file(str(tmp_path / "missing.json"), output=False)
+
+
+def test_add_json_file_optional_missing_returns_none(tmp_path):
+    result = Configuration.add_json_file(
+        str(tmp_path / "missing.json"), optional=True, output=False
+    )
+    assert result is None
+
+
+def test_add_json_file_invalid_json(tmp_path):
+    # _load_json_file catches parse errors and returns {} — no SystemExit.
+    # add_json_file then proceeds with an empty config (no models loaded).
+    bad_file = tmp_path / "bad.json"
+    bad_file.write_text("not valid json", encoding="utf-8")
+    Configuration.add_json_file(str(bad_file), output=False)
+    # No model should be registered since the file was invalid
+    assert Configuration.get("AppSettings") is None