How to mock wrong credentials?

[Achilles0509]

class AllowAllAuthHandler(ServerInterface):
    def check_auth_none(self, username):
        return AUTH_SUCCESSFUL

    def check_auth_password(self, username, password):
        return AUTH_SUCCESSFUL

    def check_auth_publickey(self, username, key):
        return AUTH_SUCCESSFUL

    def check_channel_request(self, kind, chanid):
        return OPEN_SUCCEEDED

As you can see it allows any username password combinations, so it's difficult to mock wrong credentials.