'Check that NodeTransformers can reject input.'

def test_input_rejection(self):

    expect_exception_tb = tt.AssertPrints('InputRejected:    test')
    expect_no_cell_output = tt.AssertNotPrints("'unsafe'", suppress=False)
    with expect_exception_tb:
        with expect_no_cell_output:
            ip.run_cell("'unsafe'")
    with expect_exception_tb:
        with expect_no_cell_output:
            res = ip.run_cell("'unsafe'")
    self.assertIsInstance(res.error_before_exec, InputRejected)
