Some simple snippets to do logic testing in kotlin

JUnit Test

When doing Unit testing we don’t depend on Android so here is the sample of a basic rest service test.


import org.junit.Assert.*
import org.junit.Test

 * Created by hugomatilla on 02/03/16.
class CloudUnitTest {
    // ----- Article List -----
    fun requestTopArticles() {
        val articles = RestService().fetchArticlesList()
        assertEquals(articles.size, 245)

    // ------ Exceptions -----
    fun catchMalformedUrl() {
        try {
            fail("MalformedURLException not catch");
        } catch (error: MalformedURLException) {

    // ----- Article Sections -----
    fun requestArticleSections() {
        val sections = RestService().fetchArticleSections(1)
        if (sections != null)
            assertEquals(sections.elementAt(0).title, "Section Title")
            fail("Sections is null")

Android Tests

If we need a context for example to access the data base we will need to use android tests instead of “normal” tests.

We do not need any UI testing, just the context, so we don’t need to import espresso libraries for this test. So our dependencies in the build.gradle file will need the runner and the rules.

testCompile 'junit:junit:4.12'
//instrumentation tests
androidTestCompile ""
androidTestCompile ""

Other thing that we might need is an application where the android test will “take” the context. This is easy if we are making the tests for the presentation layer (Clean Architecture). In this case I am making a test for the data layer, that is a different module and does not have any idea of what is in the presentation layer. So I can not import any activity or my “MyApplication.class” to the test. What you can do is use the Application.class. The runner will create it before running the test, and use its context. And notice that you have to call createApplication() before using application. Thanks to Kotlin instead of calling the accessors of application i.e getApplication() we can directly access to it with its property name application.

A test of the DataBase will look something like this.

class DataTests : ApplicationTestCase<Application>( {
    private var DB: Db? = null

    override fun setUp() {
        DB = Db(DbHelper(application.applicationContext, DbHelper.DB_NAME_MOCK, 1), DbMapper())

    fun test_saveArticle() {
        val article = ArticleDomain(1, "Title", "Abstract", "Thumbnail", 1, 2, "Url", "Type", emptyList())
        val result = DB!!.getArticleDetailById(1)
        if (result != null)
            assertEquals(result, article)
            fail("Return value from the data base is null")

    override fun tearDown() {

Remember that tests must start with the prefix test_ as in test_saveArticle()

To create my database instance I need to pass to the constructor a Database Helper with a context, a name of the database (I use a mock name for the tests) and a version number, and a data mapper.

And don’t forget to clear the database in the tear down of the test, so every test will start with an fresh and empty database.


Testing in Kotlin should be as easy if not easier as testing in Java. Having a snippet as a starting point is always helpful for the new comers.

You can find more in this github project