how test a kotlin class?


TDD is a modern software development process based on creation of automatic test before write code, so modern programming can’t be called in this way without test the software. In this post i want to write something about testing software written in kotlin .

Ok, after this little presentation let’s start to write some code: in the previous post on kotlin the problem was connect to mongo db and write some data. Now i want to complicate this example and the challenge is write a class (data class) and then save it into the database.

In kotlin write a data class is very simple (can find here), my data class for this example is this:

data class Person (val name:String, val surname:String, val age:Int)

Testing this class is very simple, we can test it in the same java way: with junit!

On IntelliJ create test can be done directly from the class:

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We can select which methods to test and the IDE create the skeleton for the test class:

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I saved this test class in a test folder to keep everything organized. It’s important to configure the test folder for the project:

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Now, all it’s configured, and now i can test my class! Run the test class and the result is something like this:

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gatsby-is-already-doing-great-at-the-box-office-despite-harsh-reviews      All Green! Great!


Kotlin exercise 1: Connect to MongoDB -part 2-


In the first part of this exercise we have seen how connect to a MongoDb with Java. Now that is clear how the connection can be performed, we can try to do the same with Kotlin.
Ok, no waste other time, start coding:

import com.mongodb.BasicDBObject
import com.mongodb.MongoClient
import com.mongodb.MongoException
import java.util.*

 * Created by Claudio on 01/05/16.
 * This is a main to test mongoDB connection in kotlin

fun main(args: Array<String>) {

        val mongo = MongoClient("localhost", 27017)

        val db = mongo.getDB("testDB")

        val table = db.getCollection("person")

        //Reflection example
        val person = Person("Jon","Doe",20);

        val data = person.javaClass;

        //Insert document
        val document = BasicDBObject()
        document.put("name", "mkyong")
        document.put("age", 30)
        document.put("createdDate", Date())

        /**** Find and display ****/
        val searchQuery = BasicDBObject();
        searchQuery.put("name", "mkyong");

        val cursor = table.find(searchQuery);

        while (cursor.hasNext()) {
    catch (e: UnknownHostException) {
        e.printStackTrace ( );
    } catch (e: MongoException) {


Sorry but the kotlin code isn’t highlighted

How we see the code is similar with Java example and the output is equal:

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This code can be converted from Java code with the intellij IDE function called: “Convert java code to kotlin code”. This can be reached from the search tool or vith copy and paste of java code to kotlin file:


For exercise the “Main.kt” code is was written from scratch.

In this little exercice I learned how connect to MongoDb and how code something more difficult to “hello world” in Kotlin.

A little step for mankind, a big step for a developer!


Kotlin exercise 1: Connect to MongoDB -part 1-


After the firts posts on Kotlin, i want to creating something more difficult. And i chose to try a database connection in Kotlin.

In this exercise i chose to connect my little application to a Mongo database. This choice is driven by a book that i started to read in  these days: “MongoDb in action”, because i want to know more about this type of database. So i decided to try to use both new things: kotlin and MongoDB.

This exercise is organized in this way: first part is a java test connection and operations with MongoDB then the same operations are written in Kotlin.

Ok, let’s start with code:

Firt of all create the instance of mongodb client and create te DB:

import com.mongodb.*;

import java.util.Date;

 * Created by Claudio on 30/04/16.
public class Main {

    public static void main(String[] args) {

        try {
            MongoClient mongo = new MongoClient( "localhost" , 27017 );

            DB db = mongo.getDB("testDB");

            DBCollection table;
            table = db.getCollection ("clienti");

            //Insert document
            BasicDBObject document = new BasicDBObject();
            document.put("name", "mkyong");
            document.put("age", 30);
            document.put ("createdDate", new Date ( ));

            /**** Find and display ****/
            BasicDBObject searchQuery = new BasicDBObject();
            searchQuery.put("name", "mkyong");

            DBCursor cursor = table.find(searchQuery);

            while (cursor.hasNext()) {

        } catch (UnknownHostException e) {
            e.printStackTrace ( );
        } catch (MongoException e) {


this is a little example to show how to:

  • connect to MongoDB (line 14)
  • create or get database (lines 16-19)
  • create a document (lines 22-26)
  • get insered data (lines 29-32)
  • show on standart output the datas (34-35)

The result of running this code is:

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The next part is focused on the Kotlin equivalent code.