code: def test_singleton():
      assert NA is NA
      new_NA = type(NA)()
      assert new_NA is NA
  
imports: from datetime import date, time, timedelta
  import pickle
  import numpy
  import pytest
  from pandas._libs.missing import NA
  from pandas.core.dtypes.common import is_scalar
  import pandas
  import pandas._testing
label_desc: Use image node_id 1 for calling a global function with example usage: test_singleton() without return types