Context manager for capturing output

[Wojtek Ruszczewski]

I've recently something like this (for #23929, where the output is generated by a signal handler):

@contextmanager
def capture_stdout():
    """
    Captures the ``sys.stdout`` stream, making anything written to it
    available in the stream returned as the manager's context.

    For example:

        with capture_stdout() as out:
            # Print something.
        self.assertIn("something", out.getvalue())
    """
    old_stdout = sys.stdout
    sys.stdout = out = StringIO()
    try:
        yield out
    finally:
        sys.stdout = old_stdout

Would it be better to make it public, leave it buried for the test only or don't mind testing the output in such cases at all?