code: def test_gen_train_effectiveness():
      happy = HappyGeneration("GPT-2", "sshleifer/tiny-gpt2")
      before_result = happy.eval("../data/gen/train-eval.txt")
      happy.train("../data/gen/train-eval.txt")
      after_result = happy.eval("../data/gen/train-eval.txt")
  
      assert after_result.loss < before_result.loss
  
imports: import torch
  from happytransformer import HappyGeneration, GENSettings, GENTrainArgs, GENEvalArgs
  import pytest
  from tests.run_save_load import run_save_load
  from tests import happy_gen
label_desc: Use image node_id 9 for calling a global function with example usage: test_gen_train_effectiveness() without return types