def assertStartsWith(self, s, prefix):
        """
        Assert that C{s} starts with a particular C{prefix}.

        @param s: The input string.
        @type s: C{str}
        @param prefix: The string that C{s} should start with.
        @type prefix: C{str}
        """
        self.assertTrue(s.startswith(prefix),
                        '%r is not the start of %r' % (prefix, s))

        Assert that C{s} starts with a particular C{prefix}.

        @param s: The input string.
        @type s: C{str}
        @param prefix: The string that C{s} should start with.
        @type prefix: C{str}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_failure.py