unittest测试时，testsuite只能执行第一个用例，单独的用例都可以执行，这是为什么

代码为：
class Count:

def __init__(self,a,b):
    self.a = int(a)
    self.b = int(b)

def add(self):
    return self.a + self.b

from calculator import Count
import unittest

class TestCount(unittest.TestCase):

def setUp(self):
    print('test start')

def test_add(self):
    j = Count(2,3)
    self.assertEqual(j.add(),5)

def test_add2(self):
    j = Count(41,76)
    self.assertEqual(j.add(),117)

def tearDown(self):
    print('test end')

if name == "__main__":

suite = unittest.TestSuite()
suite.addTest(TestCount('test_add2'))
suite.addTest(TestCount('test_add'))

runner = unittest.TextTestRunner()
runner.run(suite)

错误为：
Traceback (most recent call last):

File "", line 1, in
runfile('E:/python-workspace/zidonghua/unittest/testsuite_texttestrunner_calculator.py', wdir='E:/python-workspace/zidonghua/unittest')

File "C:\Users\liushu\Anaconda2\lib\site-packages\spyder\utils\site\sitecustomize.py", line 866, in runfile
execfile(filename, namespace)

File "C:\Users\liushu\Anaconda2\lib\site-packages\spyder\utils\site\sitecustomize.py", line 87, in execfile
exec(compile(scripttext, filename, 'exec'), glob, loc)

File "E:/python-workspace/zidonghua/unittest/testsuite_texttestrunner_calculator.py", line 34, in
runner.run(suite)

File "C:\Users\liushu\Anaconda2\lib\unittest\runner.py", line 151, in run
test(result)

File "C:\Users\liushu\Anaconda2\lib\unittest\suite.py", line 70, in call
return self.run(*args, **kwds)

File "C:\Users\liushu\Anaconda2\lib\unittest\suite.py", line 108, in run
test(result)

File "C:\Users\liushu\Anaconda2\lib\unittest\case.py", line 393, in call
return self.run(*args, **kwds)

File "C:\Users\liushu\Anaconda2\lib\unittest\case.py", line 368, in run
result.addSuccess(self)

File "C:\Users\liushu\Anaconda2\lib\unittest\runner.py", line 63, in addSuccess
self.stream.flush()

IOError: [Errno 9] Bad file descriptor

https://blog.csdn.net/zha6476003/article/details/80493988