What testing methods do you use for testing Kotlin code?

I use the following testing methods:

• Unit testing: Checking individual small components (functions, classes) in isolation. I use JUnit 5 or Spek.
• Integration testing: Checking the interaction between multiple components or subsystems.
• UI testing: Testing the user interface on a real device or emulator. For Android, I use Espresso or UI Automator.
• Instrumented testing: Testing that requires execution on a device or emulator. Includes UI and some types of integration testing.
• End-to-End testing: Testing the entire application from start to finish, simulating user actions.

For writing tests, I use Mockito or MockK for mocking dependencies and Hamcrest or AssertJ for writing assertions.

// Example of a unit test using JUnit 5 and MockK
import io.mockk.every
import io.mockk.mockk
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test

class MyServiceTest {

    @Test
    fun `calculateSum should return correct sum`() {
        // Mock the dependency
        val dependency: Dependency = mockk()
        every { dependency.getValue() } returns 10

        val service = MyService(dependency)
        val result = service.calculateSum(20)

        // Check the result
        assertEquals(30, result)
    }
}

class MyService(private val dependency: Dependency) {
    fun calculateSum(a: Int): Int {
        return a + dependency.getValue()
    }
}

interface Dependency {
    fun getValue(): Int
}

// Example of a UI test for Android using Espresso
import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.action.ViewActions.click
import androidx.test.espresso.assertion.ViewAssertions.matches
import androidx.test.espresso.matcher.ViewMatchers.withId
import androidx.test.espresso.matcher.ViewMatchers.withText
import androidx.test.ext.junit.rules.ActivityScenarioRule
import org.junit.Rule
import org.junit.Test

class MainActivityTest {

    @get:Rule
    var activityRule: ActivityScenarioRule<MainActivity> = ActivityScenarioRule(MainActivity::class.java)

    @Test
    fun clickingButtonChangesText() {
        // Find the button by id and click on it
        onView(withId(R.id.button)).perform(click())

        // Check that the text in TextView has changed
        onView(withId(R.id.textView)).check(matches(withText("Text changed!")))
    }
}