def test_replaceInFile(self):
        """
        L{replaceInFile} replaces data in a file based on a dict. A key from
        the dict that is found in the file is replaced with the corresponding
        value.
        """
        content = 'foo\nhey hey $VER\nbar\n'
        with open('release.replace', 'w') as outf:
            outf.write(content)

        expected = content.replace('$VER', '2.0.0')
        replaceInFile('release.replace', {'$VER': '2.0.0'})
        with open('release.replace') as f:
            self.assertEqual(f.read(), expected)


        expected = expected.replace('2.0.0', '3.0.0')
        replaceInFile('release.replace', {'2.0.0': '3.0.0'})
        with open('release.replace') as f:
            self.assertEqual(f.read(), expected)

        L{replaceInFile} replaces data in a file based on a dict. A key from
        the dict that is found in the file is replaced with the corresponding
        value.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_release.py