code: def test_cast_custom_strings(self):
      values = ("a", "b", "c", "d", "e", "f")
      boolean_type = Boolean(
          true_values=("a", "b"),
          false_values=("d", "e"),
          null_values=("c", "f"),
      )
      casted = tuple(boolean_type.cast(v) for v in values)
      self.assertSequenceEqual(
          casted, (True, True, None, False, False, None)
      )
  
imports: import datetime
  import pickle
  import unittest
  from decimal import Decimal
  import parsedatetime
  from agate.data_types import Boolean, Date, DateTime, Number, Text, TimeDelta
  from agate.exceptions import CastError
label_desc: Use image node_id 4 for calling the TestBoolean obj's underlying member method code with example usage: obj.test_cast_custom_strings() without return types