def METHOD_NAME(client, response):
    """Retrieve a related customer object from a mandate."""
    response.get(f"https://api.mollie.com/v2/customers/{CUSTOMER_ID}", "customer_single")
    response.get(
        f"https://api.mollie.com/v2/customers/{CUSTOMER_ID}/mandates/{MANDATE_ID}",
        "customer_mandate_single",
    )
    customer = client.customers.get(CUSTOMER_ID)
    mandate = customer.mandates.get(MANDATE_ID)
    customer = mandate.get_customer()
    assert isinstance(customer, Customer)
    assert customer.id == CUSTOMER_ID