code: def test_compressed(self):
      a = masked_array(np.matrix([1, 2, 3, 4]), mask=[0, 0, 0, 0])
      b = a.compressed()
      assert_equal(b, a)
      assert_(isinstance(b, np.matrix))
      a[0, 0] = masked
      b = a.compressed()
      assert_equal(b, [[2, 3, 4]])
  
imports: 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_
  from numpy.compat import pickle
label_desc: Use image node_id 6 for calling the TestMaskedMatrix obj's underlying member method code with example usage: obj.test_compressed() without return types