How would I go about unit testing this function in Kotlin?

Question

I'm pretty new to unit testing. I've been given the task of testing this code. I understand that I have to use assertEquals to check if for example if RegionData.Key.DEV returns VZCRegion.Development. Any help would be appreciated.

fun fromCakeSliceRegion(cakeSliceIndex: RegionData.Key): VZCRegion {

    return when (cakeSliceIndex) {
        RegionData.Key.DEV -> VZCRegion.Development
        RegionData.Key.EU_TEST -> VZCRegion.EuropeTest
        RegionData.Key.US_TEST -> VZCRegion.UnitedStatesTest
        RegionData.Key.US_STAGING -> VZCRegion.UnitedStatesStage
        RegionData.Key.EU_STAGING -> VZCRegion.EuropeStage
        RegionData.Key.LOCAL, RegionData.Key.EU_LIVE -> VZCRegion.Europe
        RegionData.Key.AP_LIVE, RegionData.Key.US_LIVE -> VZCRegion.UnitedStates
        RegionData.Key.PERFORMANCE, RegionData.Key.PERFORMANCE -> VZCRegion.Performance
    }

Answer 1

First of all welcome to stackoverflow!

To get started with unit testing I will recommend you to read about them in general, good starting point, another stackoverflow answer

Now back to your test. You should create a test class under your test directory, not part of your main package.

The class could look like

import org.junit.After
import org.junit.Assert
import org.junit.Before
import org.junit.Test

class TestCakeSlice {
    @Before
    fun setUp() {
        // this will run before every test
        // usually used for common setup between tests
    }

    @After
    fun tearDown() {
        // this will run after every test
        // usually reset states, and cleanup
    }

    @Test
    fun testSlideDev_returnsDevelopment() {
        val result = fromCakeSliceRegion(RegionData.Key.DEV)

        Assert.assertEquals(result, VZCRegion.Development)
    }

    @Test
    fun `fun fact you can write your unit tests like this which is easier to read`() {
        val result = fromCakeSliceRegion(RegionData.Key.DEV)

        Assert.assertEquals(result, VZCRegion.Development)
    }
}