pythonでimportすると「ImportError: cannot import name 'webdriver'」になる。

Question

実行するとエラーになります。

「ImportError: cannot import name 'webdriver'」
どうしたらいいでしょうか？

script

test_ut.py (unittest実行用)

import unittest
import selenium.webtest1

def suite():
  suite = unittest.TestSuite()
  suite.addTest(selenium.webtest1('TestCase1'))
  return suite


if __name__ == '__main__':
  runner = unittest.TextTestRunner()
  test_suite = suite()
  runner.run(test_suite)

selenium/webtest1.py　(selenium実行ファイル)

# -*- coding: utf-8 -*-
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.support.ui import Select
from selenium.common.exceptions import NoSuchElementException
from selenium.common.exceptions import NoAlertPresentException
import unittest, time, re, datetime, os

class TestCase1(unittest.TestCase):
        def setUp(self):
                self.driver = webdriver.Firefox()
                self.driver.implicitly_wait(30)
                self.base_url = "https://yahoo.co.jp/"
                self.verificationErrors = []
                self.accept_next_alert = True

        def test_untitled_test_case(self):
                driver = self.driver
                driver.get("https://yahoo.co.jp")
                print(driver.title)

        def tearDown(self):
                self.driver.quit()
                self.assertEqual([], self.verificationErrors)

if __name__ == "__main__":
        unittest.main()

単体での実行結果

# python36 selenium/webtest1.py
Yahoo! JAPAN
.
----------------------------------------------------------------------
Ran 1 test in 2.544s

OK

それをimportしたunittest側の実行結果

# python36 test_ut.py
Traceback (most recent call last):
  File "test_ut.py", line 2, in <module>
    import selenium.webtest1
  File "/ababa/selenium/webtest1.py", line 2, in <module>
    from selenium import webdriver
ImportError: cannot import name 'webdriver'

moduleとして実行しても変わらず

# python36 -m test_ut
Traceback (most recent call last):
  File "/usr/lib64/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib64/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/ababa/test_ut.py", line 2, in <module>
    import selenium.webtest1
  File "/ababa/selenium/webtest1.py", line 2, in <module>
    from selenium import webdriver
ImportError: cannot import name 'webdriver'

環境

python 3.6
centos7