Add test for missing OpenRouter API key

tests/test_game/test_config.py

@@ -0,0 +1,17 @@
+import os
+import pytest
+import importlib
+from unittest import mock
+
+import llm_postor.config  # Import initially
+
+@pytest.fixture
+def clear_env():
+    """Clear specific environment variables for testing."""
+    with mock.patch.dict(os.environ, {"OPENROUTER_API_KEY": ""}):
+        yield
+
+def test_missing_openrouter_api_key(clear_env):
+    # Reload the module to re-evaluate with the cleared environment variable
+    with pytest.raises(ValueError, match="API key is missing"):
+        importlib.reload(llm_postor.config)