code: def test_negative_masked(self):
      prot, x = self._setup(int64factory)
      negative = tfe.negative(x)
      actual = negative.reveal().to_native()
      expected = np.array([[-1, -2, -3], [-4, -5, -6]])
      np.testing.assert_array_equal(actual, expected)
  
imports: import unittest
  import numpy
  import pytest
  import tensorflow
  import tf_encrypted
  from tf_encrypted.protocol.pond import PondMaskedTensor
  from tf_encrypted.protocol.pond import PondPublicTensor
  from tf_encrypted.tensor import fixed100
  from tf_encrypted.tensor import fixed100_ni
  from tf_encrypted.tensor import int64factory
  from tf_encrypted.tensor import int100factory
  from tf_encrypted.tensor import native_factory
label_desc: Use image node_id 5 for calling the TestMasked obj's underlying member method code with example usage: obj.test_negative_masked() without return types