code: def group_names():
      return np.array(
          [
              "2021-01",
              "2021-02",
              "2021-02",
              "2021-02",
              "2021-02",
              "2021-03",
              "2021-03",
              "2021-03",
              "2021-04",
              "2021-04",
              "2021-05",
              "2021-05",
              "2021-06",
              "2021-06",
              "2021-06",
              "2021-06",
          ]
      )
  
imports: import numpy
  import pytest
  from sklearn.dummy import DummyClassifier
  from sklearn.model_selection import cross_val_score
  from mlxtend.evaluate import GroupTimeSeriesSplit
label_desc: Use image node_id 6 for calling a global function with example usage: group_names() and returns: np