Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

tests/unit/test_router_validation.py

@@ -27,7 +27,7 @@ def test_parameter_create_missing_scenario_returns_404(
 
 @pytest.mark.usefixtures("invalid_request_payloads")
 def test_parameter_create_invalid_distribution_is_422(
-    api_client: TestClient
+    api_client: TestClient,
 ) -> None:
     response = api_client.post(
         "/api/parameters/",
@@ -90,6 +90,5 @@ def test_maintenance_negative_cost_rejected_by_schema(
     payload = invalid_request_payloads["maintenance_negative_cost"]
     response = api_client.post("/api/maintenance/", json=payload)
     assert response.status_code == 422
-    error_locations = [tuple(item["loc"])
-                       for item in response.json()["detail"]]
+    error_locations = [tuple(item["loc"]) for item in response.json()["detail"]]
     assert ("body", "cost") in error_locations