def append_file(self, filename, contents):
        """Append contents to a file

        ``filename`` should be a relative path, e.g. "foo/bar/baz.txt"
        It will be translated into a full path in a tmp dir.

        Returns the full path to the file.
        """
        full_path = os.path.join(self.rootdir, filename)
        if not os.path.isdir(os.path.dirname(full_path)):
            os.makedirs(os.path.dirname(full_path))
        with open(full_path, 'a') as f:
            f.write(contents)
        return full_path
Append contents to a file

        ``filename`` should be a relative path, e.g. "foo/bar/baz.txt"
        It will be translated into a full path in a tmp dir.

        Returns the full path to the file.
        
tests/integration/test_s3.py