cpython/Lib/test/test_unittest/_test_warnings.py

# helper module for test_runner.Test_TextTestRunner.test_warnings

"""
This module has a number of tests that raise different kinds of warnings.
When the tests are run, the warnings are caught and their messages are printed
to stdout.  This module also accepts an arg that is then passed to
unittest.main to affect the behavior of warnings.
Test_TextTestRunner.test_warnings executes this script with different
combinations of warnings args and -W flags and check that the output is correct.
See #10535.
"""

import sys
import unittest
import warnings

def warnfun():
    warnings.warn('rw', RuntimeWarning)

class TestWarnings(unittest.TestCase):
    def test_other_unittest(self):
        self.assertAlmostEqual(2+2, 4)
        self.assertNotAlmostEqual(4+4, 2)

    # these warnings are normally silenced, but they are printed in unittest
    def test_deprecation(self):
        warnings.warn('dw', DeprecationWarning)
        warnings.warn('dw', DeprecationWarning)
        warnings.warn('dw', DeprecationWarning)

    def test_import(self):
        warnings.warn('iw', ImportWarning)
        warnings.warn('iw', ImportWarning)
        warnings.warn('iw', ImportWarning)

    # user warnings should always be printed
    def test_warning(self):
        warnings.warn('uw')
        warnings.warn('uw')
        warnings.warn('uw')

    # these warnings come from the same place; they will be printed
    # only once by default or three times if the 'always' filter is used
    def test_function(self):

        warnfun()
        warnfun()
        warnfun()



if __name__ == '__main__':
    with warnings.catch_warnings(record=True) as ws:
        # if an arg is provided pass it to unittest.main as 'warnings'
        if len(sys.argv) == 2:
            unittest.main(exit=False, warnings=sys.argv.pop())
        else:
            unittest.main(exit=False)

    # print all the warning messages collected
    for w in ws:
        print(w.message)