memento go language Design Patterns

memento.go

package memento

import (
	"fmt"
)

type State struct {
	Description string
}

type memento struct {
	state State
}

type originator struct {
	state State
}

func (o *originator) NewMemento() memento {
	return memento{state: o.state}
}

func (o *originator) ExtractAndStoreState(m memento) {
	//Does nothing
	o.state = m.state
}

type careTaker struct {
	mementoList []memento
}

func (c *careTaker) Add(m memento) {
	//Does nothing
	c.mementoList = append(c.mementoList, m)

}

func (c *careTaker) Memento(i int) (memento, error) {
	if len(c.mementoList) < i || i < 0 {
		return memento{}, fmt.Errorf("Index not found\n")
	}
	return c.mementoList[i], nil
}

　　

memento_test.go

package memento

import (
	"testing"
)

func TestCareTaker_add(t *testing.T) {
	originator := originator{}
	originator.state = State{Description: "Idle"}

	careTaker := careTaker{}
	mem := originator.NewMemento()
	if mem.state.Description != "Idle" {
		t.Error("Expected state was not found")
	}

	currentLen := len(careTaker.mementoList)
	careTaker.Add(mem)

	if len(careTaker.mementoList) != currentLen+1 {
		t.Error("No new elements were added on the list")
	}
}

func TestCareTaker_Memento(t *testing.T) {
	originator := originator{}
	careTaker := careTaker{}

	originator.state = State{"Idle"}
	careTaker.Add(originator.NewMemento())

	mem, err := careTaker.Memento(0)
	if err != nil {
		t.Fatal(err)
	}

	if mem.state.Description != "Idle" {
		t.Error("Unexpected state")
	}

	mem, err = careTaker.Memento(-1)

	if err == nil {
		t.Fatal("An error is expected when asking for a negative number but no error was found")
	}
}

func TestOriginator_ExtractAndStoreState(t *testing.T) {
	originator := originator{state: State{"Idle"}}
	idleMemento := originator.NewMemento()

	originator.ExtractAndStoreState(idleMemento)
	if originator.state.Description != "Idle" {
		t.Error("Unexpected state found")
	}
}