Como executar o comando mongo com o mongo-go-driver?

if cur, err = collection.Find(ctx, bson.M{"hometown": bson.M{"$exists": 1}}); err != nil {
    t.Fatal(err)
}
var doc bson.M
for cur.Next(ctx) {
    cur.Decode(&doc)
    doc["updated"] = time.Now()
    if result, err = collection.ReplaceOne(ctx, bson.M{"_id": doc["_id"]}, doc); err != nil {
        t.Fatal(err)
    }
    if result.MatchedCount != 1 || result.ModifiedCount != 1 {
        t.Fatal("replace failed, expected 1 but got", result.MatchedCount)
    }
}