What is wrong with this code snippet for generating an HTML report using HtmlTestRunner?

What is wrong with this code snippet for generating an HTML report using HtmlTestRunner?

import unittest
import HtmlTestRunner

class TestExample(unittest.TestCase):
    def test_fail(self):
        self.assertEqual(1, 2)

if __name__ == '__main__':
    unittest.main(testRunner=HtmlTestRunner.HTMLTestRunner(output=''))