檢查一個函數引發鼻測試的警告

Question

我正在使用nose編寫單元測試，我想檢查一個函數是否發出警告（函數使用warnings.warn）。這是否可以輕鬆完成？

Answer 1

def your_code(): 
    # ... 
    warnings.warn("deprecated", DeprecationWarning) 
    # ... 

def your_test(): 
    with warnings.catch_warnings(record=True) as w: 
     your_code() 
     assert len(w) > 1 

而不是僅僅檢查lenght，你可以深入的檢查，當然：

assert str(w.args[0]) == "deprecated"

在Python 2.7版或更高版本，可以與上次檢查爲做到這一點：

assert str(w[0].message[0]) == "deprecated"

Answer 2

有（至少）這樣做有兩種方式。您可以在list的warnings.WarningMessage s中測試或在您的模塊中使用mock到patch導入的warnings。

我認爲patch版本更一般。

raise_warning.py：

import warnings 

def should_warn(): 
    warnings.warn('message', RuntimeWarning) 
    print('didn\'t I warn you?') 

raise_warning_tests.py：

import unittest 
from mock import patch 
import raise_warning 

class TestWarnings(unittest.TestCase): 

    @patch('raise_warning.warnings.warn') 
    def test_patched(self, mock_warnings): 
     """test with patched warnings""" 
     raise_warning.should_warn() 
     self.assertTrue(mock_warnings.called) 

    def test_that_catches_warning(self): 
     """test by catching warning""" 
     with raise_warning.warnings.catch_warnings(True) as wrn: 
      raise_warning.should_warn() 
      # per-PEP8 check for empty sequences by their Truthiness 
      self.assertTrue(wrn)