go mgo mongodb+test example, test insert same data to unique key

mgo.go

package main

import (
	mgo "gopkg.in/mgo.v2"
	"gopkg.in/mgo.v2/bson"
	"time"
)

// ========== model

type Cargo struct {
	Id    bson.ObjectId `form:"id" bson:"_id,omitempty"`
	Value string        `form:"value" bson:"value"`
}

// ========== mongo

type MongoDB struct {
	Host             string
	Port             string
	Addrs            string
	Database         string
	EventTTLAfterEnd time.Duration
	StdEventTTL      time.Duration
	Info             *mgo.DialInfo
	Session          *mgo.Session
}

func ConfigureMongo(mongo *MongoDB) (err error) {// {{{
	mongo.Port = "27017"
	mongo.Host = "localhost"
	mongo.Addrs = mongo.Host + ":" + mongo.Port
	mongo.Database = "test"

	mongo.EventTTLAfterEnd = 1 * time.Second
	mongo.StdEventTTL = 20 * time.Minute
	mongo.Info = &mgo.DialInfo{
		Addrs:    []string{mongo.Addrs},
		Timeout:  60 * time.Second,
		Database: mongo.Database,
	}

	// first connect, and next requests only clones this session
	mongo.Session, err = mgo.DialWithInfo(mongo.Info)
	if err != nil {
		mongo.Session, err = mgo.Dial(mongo.Host)
	}
	return err
}

func (mongo *MongoDB) Drop() (err error) {
	session := mongo.Session.Clone()
	defer session.Close()

	err = session.DB(mongo.Database).DropDatabase()
	return err
}

func (mongo *MongoDB) Init() (err error) {
	session := mongo.Session.Clone()

	defer session.Close()
	session.EnsureSafe(&mgo.Safe{})

	collection := session.DB(mongo.Database).C("cargo")
	index := mgo.Index{
		Key:        []string{"value"},
		Unique:     true,
		Background: true,
		Sparse:     true,
	}
	err = collection.EnsureIndex(index)

	return err
}

// ========== methods

func (mongo *MongoDB) GetCargo() (cargos []Cargo, err error) {
	session := mongo.Session.Clone()
	defer session.Close()

	err = session.DB(mongo.Database).C("cargo").Find(bson.M{}).All(&cargos)
	return cargos, err
}

func (mongo *MongoDB) PostCargo(cargo *Cargo) (err error) { // {{{
	session := mongo.Session.Clone()

	defer session.Close()
	err = session.DB(mongo.Database).C("cargo").Insert(&cargo)
	return err
}

mgo_test.go

package main

import (
	gen "github.com/asm-jaime/gen"
	"testing"
)

func dbTest() (mongo *MongoDB) {
	mongo = &MongoDB{}

	err := ConfigureMongo(mongo)
	if err != nil {
		panic("db does not allow set any session. \n" +
			"here is a problem with config params or database")
	}

	err = mongo.Drop()
	if err != nil {
		panic("db does not allow drop.")
	}

	err = mongo.Init()
	if err != nil {
		panic("db does not allow init.")
	}

	return mongo
}

func Test2xSamePost(t *testing.T) {
	db := dbTest()

	cargo := Cargo{}
	cargo.Value = gen.StrNums(8)

	err := db.PostCargo(&cargo)
	if err != nil {
		t.Error("first insert err: ", err)
	}

	err = db.PostCargo(&cargo)
	if len(err.Error()) > 6 && err.Error()[0:6] == "E11000" {
		// fmt.Println(err)
	} else {
		t.Error("this err is not proper error, ", err)
	}
}