code: def test_keys(self):
      table = Table(
          self.rows,
          self.column_names,
          self.column_types,
          row_names="three",
      )
  
      self.assertIs(self.table.columns["one"].keys(), None)
      self.assertSequenceEqual(
          table.columns["one"].keys(), ["a", "b", "c"]
      )
  
imports: import pickle
  import unittest
  from decimal import Decimal
  from agate import Table
  from agate.data_types import Number, Text
label_desc: Use image node_id 7 for calling the TestColumn obj's underlying member method code with example usage: obj.test_keys() without return types