def METHOD_NAME(self, appconfiguration_connection_string, appconfiguration_keyvault_secret_url):
    client = self.create_client(
        appconfiguration_connection_string, keyvault_secret_url=appconfiguration_keyvault_secret_url
    )
    min_backoff = 30000
    assert min_backoff == client._refresh_timer._calculate_backoff()
    attempts = 2
    client._refresh_timer.attempts = attempts
    backoff = client._refresh_timer._calculate_backoff()
    assert backoff >= min_backoff and backoff <= (min_backoff * (1 << attempts))
    attempts = 3
    client._refresh_timer.attempts = attempts
    backoff = client._refresh_timer._calculate_backoff()
    assert backoff >= min_backoff and backoff <= (min_backoff * (1 << attempts))