'Test the log1p atom.'

def test_log1p(self):

    expr = log1p(1)
    self.assertEqual(expr.sign, s.POSITIVE)
    self.assertEqual(expr.curvature, s.CONSTANT)
    self.assertEqual(expr.size, (1, 1))
    expr = log1p((-0.5))
    self.assertEqual(expr.sign, s.NEGATIVE)
