如何使assertRaises（）打印在Python 2.7中傳遞的* args，** wargs？

Question

我在這樣的循環中使用assertRaises ：

for i in ['a', 'b', 'c']: 
    self.assertRaises(ValidationError, my_method, i)

問題是每當測試失敗時，輸出將如下所示：

  File "/bla/test.py", line 4, in test_assertion
      my_method(i)
AssertionError: ValidationError not raised

測試失敗時如何打印出i的值？ 像這樣：

  File "/bla/test.py", line 4, in test_assertion
      my_method('b')
AssertionError: ValidationError not raised

Answer 1

這是subTests上下文管理器的理想情況。 但是，這僅在python 3中可用。我認為最好的解決方案是創建自己的subTests版本。 好處是可以很容易地設置subTests的基本模擬，並且如果將subTests重新移植到python 2，則將很容易切換。

import unittest
import sys
from contextlib import contextmanager

class TestCaseWithSubTests(unittest.TestCase):

    @contextmanager
    def subTest(self, **kwargs):
        try:
            yield None
        except:
            exc_class, exc, tb = sys.exc_info()
            kwargs_desc = ", ".join("{}={!r}".format(k, v) for k, v in kwargs.items())
            new_exc = exc_class("with {}: {}".format(kwargs_desc, exc))
            raise exc_class, new_exc, tb.tb_next

class MyTest(TestCaseWithSubTests):

    def test_with_assertion_error(self):
        for i in [0, 1]:
            with self.subTest(i=i), self.assertRaises(ZeroDivisionError):
                1 / i

    def test_with_value_error(self):
        def f(i):
            raise ValueError

        for i in [0, 1]:
            with self.subTest(i=i), self.assertRaises(ZeroDivisionError):
                f(i)


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

產生以下輸出：

FE
======================================================================
ERROR: test_with_value_error (__main__.MyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\dunes\py2sub_tests.py", line 30, in test_with_value_error
    f(i)
  File "C:\Python27\lib\contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "C:\Users\dunes\py2sub_tests.py", line 30, in test_with_value_error
    f(i)
  File "C:\Users\dunes\py2sub_tests.py", line 26, in f
    raise ValueError
ValueError: with i=0: 

======================================================================
FAIL: test_with_assertion_error (__main__.MyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\dunes\py2sub_tests.py", line 22, in test_with_assertion_error
    1 / i
  File "C:\Python27\lib\contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "C:\Users\dunes\py2sub_tests.py", line 22, in test_with_assertion_error
    1 / i
AssertionError: with i=1: ZeroDivisionError not raised

----------------------------------------------------------------------
Ran 2 tests in 0.006s

FAILED (failures=1, errors=1)

Answer 2

一種解決方案是使用assertRaises()作為上下文管理器。

with self.assertRaises(ValidationError):
    my_method(i)
    print("Failed when i was",i)

僅當my_method()行成功通過時，print語句才會執行，因此當測試失敗時，它將顯示為輸出。 有點my_method() ，但確實有效（除非my_method()拋出不是ValidationError錯誤）。