'Test the kron atom.'

def test_kron(self):

    a = np.ones((3, 2))
    b = Parameter(2, sign='positive')
    expr = kron(a, b)
    assert expr.is_positive()
    self.assertEqual(expr.size, (6, 2))
    b = Parameter(2, sign='negative')
    expr = kron(a, b)
    assert expr.is_negative()
    with self.assertRaises(Exception) as cm:
        kron(self.x, (-1))
    self.assertEqual(str(cm.exception), 'The    first    argument    to    kron    must    be    constant.')
