code: def test_matrix(self):
      # Test consistency with unmasked version.  If we ever deprecate
      # matrix, this test should either still pass, or both actual and
      # expected should fail to be build.
      actual = mr_["r", 1, 2, 3]
      expected = np.ma.array(np.r_["r", 1, 2, 3])
      assert_array_equal(actual, expected)
  
      # outer type is masked array, inner type is matrix
      assert_equal(type(actual), type(expected))
      assert_equal(type(actual.data), type(expected.data))
  
imports: import pickle
  import numpy
  from numpy.testing import assert_warns
  from numpy.ma.testutils import assert_, assert_equal, assert_raises, assert_array_equal
  from numpy.ma.core import masked_array, masked_values, masked, allequal, MaskType, getmask, MaskedArray, nomask, log, add, hypot, divide
  from numpy.ma.extras import mr_
label_desc: Use image node_id 2 for calling the TestConcatenator obj's underlying member method code with example usage: obj.test_matrix() without return types