code: def test_gain(self):
      path = get_asset_path("steam-train-whistle-daniel_simon.wav")
      data, _ = load_wav(path)
      result = F.gain(data, 3)
      self.assert_sox_effect(result, path, ["gain", 3])
  
imports: import torch
  import torchaudio.functional
  from torchaudio_unittest.common_utils import get_asset_path, get_whitenoise, load_wav, save_wav, skipIfNoExec, skipIfNoSox, sox_utils, TempDirMixin, TorchaudioTestCase
label_desc: Use image node_id 4 for calling the TestFunctionalFiltering obj's underlying member method code with example usage: obj.test_gain() without return types