Python3 在使用HTMLTestRunner时，报错：raise TypeError("{} is not callable".format(repr(test)))

代码如下：

import pymysql
import unittest
import time
import unittest.suite
import HTMLTestRunner
import sys
def hell(a):
    print(a)
    return a


testunit = unittest.TestSuite()
testunit.addTest(hell('ad'))

filename = '/Users/vivi/Downloads/aa.html'
fp = open(filename, 'wb')  # 之前写的是file(filename,'wb')，但是无法识别file方法，改成open，OK！
runner = HTMLTestRunner.HTMLTestRunner(stream=fp, title=u'print', description=u'简单')
runner.run(testunit)

运行后报错：

Traceback (most recent call last):
  File "/Applications/Python 3.5/……/B.py", line 30, in <module>
    testunit.addTest(hell('ad'))
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/unittest/suite.py", line 47, in addTest
    raise TypeError("{} is not callable".format(repr(test)))
TypeError: 'ad' is not callable