code: def test_mse():
      predictions = pd.Series([1.0, 2.0, 0.0])
      targets = pd.Series([1.0, 2.0, 3.0])
      result = mse().eval_fn(predictions, targets, {})
      assert result.aggregate_results["mean_squared_error"] == 3.0
  
imports: from unittest import mock
  import pandas
  import pytest
  from mlflow.metrics import MetricValue, ari_grade_level, exact_match, f1_score, flesch_kincaid_grade_level, mae, mape, max_error, mse, ndcg_at_k, precision_at_k, precision_score, r2_score, recall_at_k, recall_score, rmse, rouge1, rouge2, rougeL, rougeLsum, toxicity
label_desc: Use image node_id 13 for calling a global function with example usage: test_mse() without return types