You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: macvlan_setup_test.go
    path of file: ./repos/docker-ce/components/engine/libnetwork/drivers/macvlan
    
    the code of the file until where you have to start completion: //go:build linux
// +build linux

package macvlan

import (
	"testing"

	"github.com/vishvananda/netlink"
)

// TestValidateLink tests the parentExists function
func TestValidateLink(t *testing.T) {
	validIface := "lo"
	invalidIfa
    
func TestValidateLink(t *testing.T) {
	validIface := "lo"
	invalidIface := "foo12345"

	// test a valid parent interface validation
	if ok := parentExists(validIface); !ok {
		t.Fatalf("failed validating loopback %s", validIface)
	}
	// test an invalid parent interface validation
	if ok := parentExists(invalidIface); ok {
		t.Fatalf("failed to invalidate interface %s", invalidIface)
	}
}