docs: def within_set(df, items=None):
      """
      Assert that df is a subset of items
  
      Parameters
      ==========
  
      df : DataFrame
      items : dict
          mapping of columns (k) to array-like of values (v) that
          ``df[k]`` is expected to be a subset of
      """
      for k, v in items.items():
          if not df[k].isin(v).all():
              raise AssertionError
      return df