上一章学习了pytest的基本用法，今天学习一下断言。

1、assert 基本用法

unitest单元测试框架中提供了丰富的断言方法，如assertEqual()、assertIn()、assertTrue()、assertIs()等，但是pytest没有。直接使用Python的assert进行断言

  1. # MyPytest.py
  2. import pytest
  4. def inc(x):
  5.     return x+1
  7. # 判断结果不等于5
  8. def test_inc_01():
  9.     assert inc(3) != 5
  11. # 判断结果等于4
  12. def test_inc_02():
  13.     assert inc(3) == 4
  15. # 判断结果小于等于5
  16. def test_inc_03():
  17.     assert inc(3) <= 5
  19. # 判断结果包含在列表内
  20. def test_inc_04():
  21.     assert inc(3)  in  [1,2,3,4]
  24. # 判断结果不为True
  25. def test_inc_06():
  26.     a = 1 
  27.     assert a ==  True
  28.     assert a is not  True
  32. if __name__ =="__main__":
  33.     pytest.main(['MyPytest.py'])

执行结果：

  1. collected 5 items
  3. MyPytest.py .....                                                        [100%]
  5. ============================== 5 passed in 0.08s ==============================
  7. ***Repl Closed***

2、assert断言失败提示

当我们为了脚本报错后更容易的定位到原因时候，可以在断言的地方输出断言失败提示信息，比如：

  1. # MyPytest.py
  2. import pytest
  4. def division(x):
  5.     return 100/x
  8. def test_division_01():
  9.     res = division(3)
  10.     assert res == 50 , f"判断 res 为50 ，当前 res 的值为{res}" 
  13. if __name__ =="__main__":
  14.     pytest.main(['MyPytest.py'])

执行结果：

  1. collected 1 item
  3. MyPytest.py F                                                            [100%]
  5. ================================== FAILURES ===================================
  6. ______________________________ test_division_01 _______________________________
  8.     def test_division_01():
  9.         res = division(3)
  10. >       assert res == 50 , f"判断 res 为50 ，当前 res 的值为{res}"
  11. E       AssertionError: 判断 res 为50 ，当前 res 的值为33.333333333333336
  12. E       assert 33.333333333333336 == 50
  14. MyPytest.py:10: AssertionError
  15. =========================== short test summary info ===========================
  16. FAILED MyPytest.py::test_division_01 - AssertionError: 判断 res 为50 ，当前 r...
  17. ============================== 1 failed in 0.21s ==============================
  19. ***Repl Closed***

3、预期内异常报错断言

有时候一些场景我们明知道它会报错，也知道这种报错，是正常的预期，比如：

  1. # MyPytest.py
  2. import pytest
  4. def division(x):
  5.     return 100/x
  8. def test_division_01():
  9.     res = division(0)
  12. if __name__ =="__main__":
  13.     pytest.main(['MyPytest.py'])

执行结果：

  1. collected 1 item
  2. MyPytest.py F                                                            [100%]
  4. ================================== FAILURES ===================================
  5. ______________________________ test_division_01 _______________________________
  6.     def test_division_01():
  7. >       res = division(0)
  8. MyPytest.py:9: 
  9. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  10. x = 0
  11.     def division(x):
  12. >       return 100/x
  13. E       ZeroDivisionError: division by zero
  14. MyPytest.py:5: ZeroDivisionError
  15. =========================== short test summary info ===========================
  16. FAILED MyPytest.py::test_division_01 - ZeroDivisionError: division by zero
  17. ============================== 1 failed in 0.21s ==============================
  19. ***Repl Closed***

100 \ 0的时候报错ZeroDivisionError: division by zero。为了对这种异常场景进行断言，我们需要使用pytest.raises，用法如下：

  1. # MyPytest.py
  2. import pytest
  4. def division(x):
  5.     return 100/x
  7. def test_division_01():
  8.     with pytest.raises(ZeroDivisionError) as e:
  9.         division(0)
  10.     assert e.type == ZeroDivisionError
  11.     assert "division by zero" in str(e.value) 
  13. if __name__ =="__main__":
  14.     pytest.main(['MyPytest.py'])

注意：断言 type 的时候，异常类型是不需要加引号的，断言 value 值的时候需转 str

4、非预期内异常

如果我们不知道预期异常的是什么，我们可以使用match和raise进行自定义异常

  1. # MyPytest.py
  2. import pytest
  4. def division(x):
  5.     if x == 0:
  6.         raise ValueError('value not 0 or None')
  7.     if isinstance(x,str):
  8.         raise TypeError('value not String')
  9.     return 100/x
  12. def test_division_01():
  13.     with pytest.raises(ValueError,match = 'value not 0 or None') as e:
  14.         division(0)
  15.     assert e.type == ValueError
  16.     assert "value not 0 or None" in str(e.value) 
  19. def test_division_02():
  20.     with pytest.raises(TypeError,match = 'value not String') as e:
  21.         division("String")
  22.     assert e.type == TypeError
  23.     assert "value not String" in str(e.value) 
  25. if __name__ =="__main__":
  26.     pytest.main(['MyPytest.py'])

5、pytest-assume插件

pytest-assume是一个可以允许pytest测试用例中执行多个失败的断言的插件。
安装

pip install pytest-assume

对比assert ：

  1. import pytest
  3. def inc(x):
  4.     return x+1
  6. # assert断言
  7. def test_inc_01():
  8.     assert inc(3) == 5
  9.     assert inc(3) == 4
  10.     assert inc(3) == 3
  13. # pytest.assume断言
  14. def test_inc_02():
  15.     pytest.assume(inc(3) == 5)
  16.     pytest.assume(inc(3) == 4)
  17.     pytest.assume(inc(3) == 3)
  20. if __name__ =="__main__":
  21.     pytest.main(['MyPytest.py'])

结果：

  1. collected 2 items
  3. MyPytest.py FF                                                           [100%]
  5. ================================== FAILURES ===================================
  6. _________________________________ test_inc_01 _________________________________
  7.     def test_inc_01():
  8. >       assert inc(3) == 5
  9. E       assert 4 == 5
  10. E        +  where 4 = inc(3)
  11. MyPytest.py:8: AssertionError
  12. _________________________________ test_inc_02 _________________________________
  14. tp = <class 'pytest_assume.plugin.FailedAssumption'>, value = None, tb = None
  15.     def reraise(tp, value, tb=None):
  16.         try:
  17.             if value is None:
  18.                 value = tp()
  19.             if value.__traceback__ is not tb:
  20. >               raise value.with_traceback(tb)
  21. E               pytest_assume.plugin.FailedAssumption: 
  22. E               2 Failed Assumptions:
  23. E               
  24. E               MyPytest.py:15: AssumptionFailure
  25. E               >>    pytest.assume(inc(3) == 5)
  26. E               AssertionError: assert False
  27. E               
  28. E               MyPytest.py:17: AssumptionFailure
  29. E               >>    pytest.assume(inc(3) == 3)
  30. E               AssertionError: assert False
  32. D:\software\python\lib\site-packages\six.py:718: FailedAssumption
  33. =========================== short test summary info ===========================
  34. FAILED MyPytest.py::test_inc_01 - assert 4 == 5
  35. FAILED MyPytest.py::test_inc_02 - pytest_assume.plugin.FailedAssumption: 
  36. ============================== 2 failed in 0.26s ==============================
  37. ***Repl Closed***

对比发现，pytest.assume在第一个断言失败的情况下继续执行后续的断言，不会终止~