Mocking an SSLError in Python

I've been dealing with the ssl.SSLError: [SSL: UNSAFE_LEGACY_RENEGOTIATION_DISABLED] unsafe legacy renegotiation disabled issue described here. As part of the fix, I'm attempting to write in exception-handling for the exception:

try:
    return req()
except (ssl.SSLError, RSSLError) as ssl_err:
    print(ssl_err)
    if "UNSAFE_LEGACY_RENEGOTIATION_DISABLED" in str(ssl_err):
        ctx = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)
        ctx.options |= 0x4
        self._sess.mount("https://", CustomHttpAdapter(ctx))
        return req()
    raise

The issue I'm having is testing it. I've tried doing this:

err = SSLError()
err.reason = "UNSAFE_LEGACY_RENEGOTIATION_DISABLED"

but this prints as (). How do I create a mock SSLError that I can use to test this code?

You need to pass the string as your argument to the constructor:

>>> from ssl import SSLError
>>> error = SSLError("UNSAFE_LEGACY_RENEGOTIATION_DISABLED")
>>> print(error)
('UNSAFE_LEGACY_RENEGOTIATION_DISABLED',)