#Percona MongoDB Go driver

WIP NOT ALL INTERFACES HAVE BEEN IMPLEMENTED YET

This is just a collection of interfaces around the structures in mgo, (Rich MongoDB driver for Go) to be able to mock methods in the driver.

The motivation for this package is that there are certain things, like errors, that cannot be tested/reproduced using a real db connection.
Also, for some of our tests we need very specific MongoDB configuration. Tests for some parts of our code need 2 replicas, config and mongos servers and that's not easily reproducible in all CI environments.

##How to use it

This package is almost a drop-in replacement with the exception that you need to use the Dialer interface.

package main

import (
    "fmt"
    "log"

    "github.com/percona/pmgo"
    "gopkg.in/mgo.v2/bson"
)

type User struct {
    ID   int    `bson:"id"`
    Name string `bson:"name"`
}

func main() {
    dialer := pmgo.NewDialer()
    session, err := dialer.Dial("localhost")
    if err != nil {
        print(err)
        return
    }

    user, err := getUser(session, 1)
    if err != nil {
        log.Printf("error reading the user from the db: %s", err.Error())
        return
    }
    fmt.Printf("User: %+v\n", user)

}

func getUser(session pmgo.SessionManager, id int) (*User, error) {
    var user User
    err := session.DB("test").C("testc").Find(bson.M{"id": id}).One(&user)

    if err != nil {
        return nil, err
    }

    return &user, nil
}

###How to write unitary tests (mocking interfaces)

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "reflect"
    "testing"

    "gopkg.in/mgo.v2/bson"

    "github.com/golang/mock/gomock"
    "github.com/percona/pmgo"
    "github.com/percona/pmgo/pmgomock"
)

var Server pmgo.DBTestServer

func TestGetUser(t *testing.T) {

    ctrl := gomock.NewController(t)
    defer ctrl.Finish()

    user := User{
        ID:   1,
        Name: "Zapp Brannigan",
    }

    // Mock up a database, session, collection and a query and set
    // expected/returned values for each type
    query := pmgomock.NewMockQueryManager(ctrl)
    query.EXPECT().One(gomock.Any()).SetArg(0, user).Return(nil)

    collection := pmgomock.NewMockCollectionManager(ctrl)
    collection.EXPECT().Find(bson.M{"id": 1}).Return(query)

    database := pmgomock.NewMockDatabaseManager(ctrl)
    database.EXPECT().C("testc").Return(collection)

    session := pmgomock.NewMockSessionManager(ctrl)
    session.EXPECT().DB("test").Return(database)

    // Call the function we want to test. It will use the mocked interfaces
    readUser, err := getUser(session, 1)
   
     if err != nil {
         t.Errorf("getUser returned an error: %s\n", err.Error())
     }

     if !reflect.DeepEqual(*readUser, user) {
         t.Errorf("Users don't match. Got %+v, want %+v\n", readUser, user)
     }
}

###How to write integration tests
A not so well known testing method is the use of mgo's dbtest server.
dbtest starts a new MongoDB instance (mongo binary must be in the path), using a temporary directory as dbpath and then on Stop() it will clean all testing data.
pmgo also has interfaces for dbtest.DBServer to use in integration tests:

func TestIntegration(t *testing.T) {
    setup()

    readUser, err := getUser(Server.Session(), 1)
    if err != nil {
        t.Errorf("getUser returned an error: %s\n", err.Error())
    }

    if !reflect.DeepEqual(*readUser, mockUser()) {
        t.Errorf("Users don't match. Got %+v, want %+v\n", readUser, mockUser())
    }

    tearDown()
}

func setup() {
    os.Setenv("CHECK_SESSIONS", "0")
    tempDir, _ := ioutil.TempDir("", "testing")
    Server = pmgo.NewDBServer()
    Server.SetPath(tempDir)

    session := Server.Session()
    // load some fake data into the db
    session.DB("test").C("testc").Insert(mockUser())
}

func mockUser() User {
    return User{
                 ID:   1,
                 Name: "Zapp Brannigan",
               }

}

func tearDown() {
    Server.Session().Close()
    Server.Session().DB("samples").DropDatabase()
    Server.Stop()
}

Generating new mocks

If you update a file to add more functions, you can create new mocks by running:

mockgen -source <path>/pmgo/collection.go -destination=<path>/pmgo/pmgomock/collection.go -package pmgomock -imports ".=github.com/percona/pmgo"