code: def test_set_fields_mask(self):
      # Tests setting the mask of a field.
      base = self.base.copy()
      # This one has already a mask....
      mbase = base.view(mrecarray)
      mbase["a"][-2] = masked
      assert_equal(mbase.a, [1, 2, 3, 4, 5])
      assert_equal(mbase.a._mask, [0, 1, 0, 1, 1])
      # This one has not yet
      mbase = fromarrays(
          [np.arange(5), np.random.rand(5)],
          dtype=[("a", int), ("b", float)],
      )
      mbase["a"][-2] = masked
      assert_equal(mbase.a, [0, 1, 2, 3, 4])
      assert_equal(mbase.a._mask, [0, 0, 0, 1, 0])
  
imports: import pickle
  import numpy
  import numpy.ma
  from numpy.ma import masked, nomask
  from numpy.testing import temppath
  from numpy._core.records import recarray, fromrecords, fromarrays
  from numpy.ma.mrecords import MaskedRecords, mrecarray, fromarrays, fromtextfile, fromrecords, addfield
  from numpy.ma.testutils import assert_, assert_equal, assert_equal_records
label_desc: Use image node_id 4 for calling the TestMRecords obj's underlying member method code with example usage: obj.test_set_fields_mask() without return types