def tenant_is_enabled(tenant_id, get_config_value):
    """
    Feature-flag test: is the given tenant enabled for convergence?

    :param str tenant_id: A tenant's ID, which may or may not be present in the
        "convergence-tenants" portion of the configuration file.
    :param callable get_config_value: config key -> config value.
    """
    disabled_tenant_ids = get_config_value("non-convergence-tenants")
    if disabled_tenant_ids == 'none':
        return True
    if disabled_tenant_ids is not None:
        return (tenant_id not in disabled_tenant_ids)
    return True