[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': "Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:from statsmodels.tsa.stattools import adfuller\ndef stationarity_test(country, case):\n    timeseries = train[train['Country_Region'] == country].groupby('Date')['ConfirmedCases', 'Fatalities'].sum().reset_index()\n    #Perform Dickey-Fuller test:\n    print('Results of Dickey-Fuller Test:')\n    dftest = adfuller(timeseries[case], autolag='AIC')\n    dfoutput = pd.Series(dftest[0:4], index=['Test Statistic','p-value',\n                                             '#Lags Used',\n                                             'Number of Observations Used'])\n    for key,value in dftest[4].items():\n        dfoutput['Critical Value (%s)'%key] = value\n    print (dfoutput)"}, {'role': 'assistant', 'content': 'evaluation'}]