关于python：PyCharm 2018中关于测试失败的两个回溯

Two tracebacks on test failure in PyCharm 2018

我在site_tests.py文件中有简单的测试：

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import unittest

class SiteTests(unittest.TestCase):

def test(self):
self.assertEqual('a', 'b')

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

当我使用默认的pycharm配置运行"unittest in test_site.py"时，我得到：

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Testing started at 23:45 ...
C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\python.exe"C:\Program Files\JetBrains\PyCharm Community Edition 2018.1.3\helpers\pycharm\_jb_unittest_runner.py" --path C:/testSiteDemoTests/site_tests.py
Launching unittests with arguments python -m unittest C:/testSiteDemoTests/site_tests.py in C:\testSiteDemoTests

b != a

Expected :a
Actual :b
<Click to see difference>

Traceback (most recent call last):
File"C:\Program Files\JetBrains\PyCharm Community Edition 2018.1.3\helpers\pycharm\teamcity\diff_tools.py", line 32, in _patched_equals
old(self, first, second, msg)
File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 829, in assertEqual
assertion_func(first, second, msg=msg)
File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 1202, in assertMultiLineEqual
self.fail(self._formatMessage(msg, standardMsg))
File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 670, in fail
raise self.failureException(msg)
AssertionError: 'a' != 'b'
- a
+ b

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 59, in testPartExecutor
yield
File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 605, in run
testMethod()
File"C:\testSiteDemoTests\site_tests.py", line 7, in test
self.assertEqual('a', 'b')

Ran 1 test in 0.000s

FAILED (failures=1)

Process finished with exit code 1

最后一部分非常有趣，因为运行这个文件时不使用_jb_unittest_runner.py，所以C:\testSite>python lost_hat_tests.py输出正常：

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F
======================================================================
FAIL: test (__main__.SiteTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File"lost_hat_tests.py", line 7, in test
self.assertEqual('a', 'b')
AssertionError: 'a' != 'b'
- a
+ b

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)

有简单的答案为什么第二条信息出现在Pycharm Runner中吗？

我还使用_jb_unittest_runner.py在控制台中运行测试-hmm two testsuites-有趣

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C:\testSiteDemoTests>python"C:\Program Files\JetBrains\PyCharm Community Edition 2018.1.3\helpers\pycharm\_jb_unittest_runner.py" --path C:/testSiteDemoTests/site_tests.py
##teamcity[enteredTheMatrix timestamp='2018-05-20T23:59:59.931']
Launching unittests with arguments python -m unittest C:/testSiteDemoTests/site_tests.py in C:\testSiteDemoTests

##teamcity[testCount timestamp='2018-05-20T23:59:59.946' count='1']
##teamcity[testSuiteStarted timestamp='2018-05-20T23:59:59.946' locationHint='python<C:\testSiteDemoTests>://site_tests' name='site_tests' nodeId='1' parentNodeId='0']
##teamcity[testSuiteStarted timestamp='2018-05-20T23:59:59.946' locationHint='python<C:\testSiteDemoTests>://site_tests.SiteTests' name='SiteTests' nodeId='2' parentNodeId='1']
##teamcity[testStarted timestamp='2018-05-20T23:59:59.962' captureStandardOutput='true' locationHint='python<C:\testSiteDemoTests>://site_tests.SiteTests.test' name='test' nodeId='3' parentNodeId='2']
##teamcity[testFailed timestamp='2018-05-20T23:59:59.977' actual='b' details='Traceback (most recent call last):|n File"C:\Program Files\JetBrains\PyCharm Community Edition 2018.1.3\helpers\pycharm\teamcity\diff_tools.py", line 32, in _patched_equals|n old(
self, first, second, msg)|n File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 829, in assertEqual|n assertion_func(first, second, msg=msg)|n File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\
lib\unittest\case.py", line 1202, in assertMultiLineEqual|n self.fail(self._formatMessage(msg, standardMsg))|n File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 670, in fail|n raise self.failureException(msg)
|nAssertionError: |'a|' != |'b|'|n- a|n+ b|n|n|nDuring handling of the above exception, another exception occurred:|n|nTraceback (most recent call last):|n File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 59, in t
estPartExecutor|n yield|n File"C:\Users\testSite\AppData\Local\Programs\Python\Python36-32\lib\unittest\case.py", line 605, in run|n testMethod()|n File"C:\testSiteDemoTests\site_tests.py", line 7, in test|n self.assertEqual(|'a|', |'b|')|n' e
xpected='a' locationHint='python<C:\testSiteDemoTests>://site_tests.SiteTests.test' message='|nb != a|n' name='test' nodeId='3' parentNodeId='2' type='comparisonFailure']
##teamcity[testFinished timestamp='2018-05-20T23:59:59.977' duration='30' locationHint='python<C:\testSiteDemoTests>://site_tests.SiteTests.test' name='test' nodeId='3' parentNodeId='2']

Ran 1 test in 0.031s

FAILED (failures=1)
##teamcity[testSuiteFinished timestamp='2018-05-20T23:59:59.977' locationHint='python<C:\testSiteDemoTests>://site_tests.SiteTests' name='SiteTests' nodeId='2' parentNodeId='1']
##teamcity[testSuiteFinished timestamp='2018-05-20T23:59:59.977' locationHint='python<C:\testSiteDemoTests>://site_tests' name='site_tests' nodeId='1' parentNodeId='0']

如果在第一个异常处理程序或finally子句中引发了另一个异常，则此消息将显示在python 3中的异常格式中：

A similar mechanism works implicitly if an exception is raised inside an exception handler or a finally clause: the previous exception is then attached as the new exception’s __context__ attribute

在pycharm中的测试上设置一个断点，然后进一步进入机器显示在哪里抛出了第二个异常。_jb_unittest_runner修补unittest中的assert方法：

PyCharm Community Edition\helpers\pycharm\_jb_unittest_runner.py：

1	from teamcity import unittestpy

PyCharm Community Edition\helpers\pycharm\teamcity\unittestpy.py：

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def run(self, test):
<...>
patch_unittest_diff(subtest_filter)
<...>

PyCharm Community Edition\helpers\pycharm\teamcity\diff_tools.py：

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def patch_unittest_diff(<...>):

old = unittest.TestCase.assertEqual

def _patched_equals(self, first, second, msg=None):
try:
old(self, first, second, msg)
return
except AssertionError as native_error:
if not test_filter or test_filter(self):
error = EqualsAssertionError(first, second, msg)
if error.can_be_serialized():
raise error
raise native_error

unittest.TestCase.assertEqual = _patched_equals