Testing custom exceptions in Kotlin with JUnit - kotlin

Question

I have the following class
data class CarDefects(
private val _carModel: CarModel,
private val _affectedYearsOfIssue: List<Year>,
private val _defectCode: String
) {
init {
validateDefectCode(_defectCode)
}
}
Validating function
fun validateDefectCode(defectCode: String) {
val pattern = Pattern.compile("^[a-zA-Z0-9-]*\$")
val m = pattern.matcher(defectCode)
if (defectCode.length !in 4..4) {
throw InvalidDefectCodeException(defectCode, "Defect code must be 4 characters long")
}
if (!m.matches()) {
throw InvalidDefectCodeException(defectCode, "Defect code can only contain alphanumeric characters")
}
}
And the exception class:
class InvalidDefectCodeException(_defectCode:String, message:String):
IllegalArgumentException("Invalid defect code $_defectCode. $message") {
}
I'm trying to test the validating function with JUnit
import car.exceptions.InvalidDefectCodeException
import car.validators.carDefectsValidators.validateDefectCode
import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
import java.time.Year
import kotlin.test.assertFailsWith
internal class CarDefectsTest {
val carModel = CarModel(Brand.BMW, "X5", 199219)
val carModel2 = CarModel(Brand.AUDI, "X434", 199219)
val defect = CarDefects(carModel, listOf(Year.of(2020), Year.of(2021)), "SE2#")
val defect2 = CarDefects(carModel2, listOf(Year.of(2020), Year.of(2021)), "122F4")
#Test
fun testDefectCodeExceptions() {
val exception = Assertions.assertThrows(InvalidDefectCodeException::class.java) {
validateDefectCode(defect.getDefectCode())
}
}
#Test
fun testDefectCodeExceptions2() {
assertFailsWith<InvalidDefectCodeException> {
validateDefectCode(defect2.getDefectCode())
}
}
}
Both tests fail, however expected exceptions are still thrown, from what i understand shouldn't both tests pass?
I've already seen the following post: Test expected exceptions in Kotlin

Answer 1

Inside class CarDefects, you're having this init block:
init {
validateDefectCode(_defectCode)
}
Hence, the exception will be thrown during construction.
Let's test the constructor instead with a stripped down CarDefects class. The following tests are passing on my computer.
import car.exceptions.InvalidDefectCodeException
import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
import kotlin.test.assertFailsWith
data class CarDefects(
private val defectCode: String
) {
init {
validateDefectCode(defectCode)
}
}
internal class CarDefectsTest {
#Test
fun testDefectCodeExceptions() {
Assertions.assertThrows(InvalidDefectCodeException::class.java) {
CarDefects(defectCode = "SE2#")
}
}
#Test
fun testDefectCodeExceptions2() {
assertFailsWith<InvalidDefectCodeException> {
CarDefects(defectCode = "122F4")
}
}
}