docs: use official mongo driver with latest version (#334)

Updates the mongodb example to use the official mongodb db drivers
(go.mongodb.org/mongo-driver/mongo) as mgo is currently unmaintained.

examples/MongoDB.md

@@ -1,32 +1,80 @@
 ```go
-var db *mgo.Session
-var err error
+package mongodb
 
-pool, err := dockertest.NewPool("")
-if err != nil {
-    log.Fatalf("Could not connect to docker: %s", err)
-}
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"testing"
 
-resource, err := pool.Run("mongo", "3.0", nil)
-if err != nil {
-    log.Fatalf("Could not start resource: %s", err)
-}
+	"github.com/ory/dockertest/v3"
+	"github.com/ory/dockertest/v3/docker"
+	"go.mongodb.org/mongo-driver/mongo"
+	"go.mongodb.org/mongo-driver/mongo/options"
+)
 
-// exponential backoff-retry, because the application in the container might not be ready to accept connections yet
-if err := pool.Retry(func() error {
-    var err error
-    db, err = mgo.Dial(fmt.Sprintf("localhost:%s", resource.GetPort("27017/tcp")))
-    if err != nil {
-        return err
-    }
-
-    return db.Ping()
-}); err != nil {
-    log.Fatalf("Could not connect to docker: %s", err)
-}
+var dbClient *mongo.Client
+
+func TestMain(m *testing.M) {
+	pool, err := dockertest.NewPool("")
+	if err != nil {
+		log.Fatalf("Could not connect to docker: %s", err)
+	}
+
+	// pull mongodb docker image for version 5.0
+	resource, err := pool.RunWithOptions(&dockertest.RunOptions{
+		Repository: "mongo",
+		Tag:        "5.0",
+		Env: []string{
+			// username and password for mongodb superuser
+			"MONGO_INITDB_ROOT_USERNAME=root",
+			"MONGO_INITDB_ROOT_PASSWORD=password",
+		},
+	}, func(config *docker.HostConfig) {
+		// set AutoRemove to true so that stopped container goes away by itself
+		config.AutoRemove = true
+		config.RestartPolicy = docker.RestartPolicy{
+			Name: "no",
+		}
+	})
+	if err != nil {
+		log.Fatalf("Could not start resource: %s", err)
+	}
+
+	// exponential backoff-retry, because the application in the container might not be ready to accept connections yet
+	err = pool.Retry(func() error {
+		var err error
+		dbClient, err = mongo.Connect(
+			context.TODO(),
+			options.Client().ApplyURI(
+				fmt.Sprintf("mongodb://root:password@localhost:%s", resource.GetPort("27017/tcp")),
+			),
+		)
+		if err != nil {
+			return err
+		}
+		return dbClient.Ping(context.TODO(), nil)
+	})
 
-// When you're done, kill and remove the container
-if err = pool.Purge(resource); err != nil {
-    log.Fatalf("Could not purge resource: %s", err)
+	if err != nil {
+		log.Fatalf("Could not connect to docker: %s", err)
+	}
+
+	// run tests
+	code := m.Run()
+
+	// When you're done, kill and remove the container
+	if err = pool.Purge(resource); err != nil {
+		log.Fatalf("Could not purge resource: %s", err)
+	}
+
+	// disconnect mongodb client
+	if err = dbClient.Disconnect(context.TODO()); err != nil {
+		panic(err)
+	}
+
+	os.Exit(code)
 }
+
 ```