gistfile1.txt

main.go: -----------------------------

package main

import (
	"fmt"
	"github.com/mgencur/awesomeProject/upgrade"
	_ "github.com/mgencur/awesomeProject/upgrade/registerplugin"
	)

func main() {
	if upgrade.Upgradable == nil {
		fmt.Println("is nil")
		upgrade.Upgradable = defaultUpgrade{}
	}
	upgrade.Upgradable.Upgrade()
}

type defaultUpgrade struct {}

func (l defaultUpgrade) Upgrade() {
	fmt.Println("Default upgrade")
}

func (l defaultUpgrade) Downgrade() {
	fmt.Println("Default downgrade")
}

upgrade/upgradable.go: -------------------------------

package upgrade

type upgradable interface {
	Upgrade()
	Downgrade()
}

var Upgradable upgradable

upgrade/registerplugin/register.go: ------------------------

package plugin

// By default this will be empty, but a plugin can be registered by importing a package with that plugin here, or the user can create another file in this package with the import
import _ "github.com/mgencur/awesomeProject/plugin"

plugin/plugin.go: ---------------------------------------------------------

package plugin

import (
	"fmt"
	"github.com/mgencur/awesomeProject/upgrade"
	"testing"
)

type upgrade2 struct {}

func (l upgrade2) Upgrade() {
	fmt.Println("New upgrade")
}

func (l upgrade2) Downgrade() {
	fmt.Println("New downgrade")
}

type UpgradeSuite struct {
	PreUpgradeTests []UpgradeTestsElement
}

type UpgradeTestsElement interface {
	Name()    string
	Handler() func(t *testing.T)
}

func init() {
	fmt.Println("Init done")
	upgrade.Upgradable = upgrade2{}  // here the implementation is switched to a new one
}