Solution: Specify expectations
fun Notifier.notifyUser(user: User?) {
user ?: return
// or
// if(user == null) return
if(!checkId(user.id)) throw IncorrectId()
require(user.name != null) {
"Name cannot be null"
}
require(user.surname != null) {
"Surname cannot be null"
}
check(initialized) {
"Notifier is not initialized"
}
val result = notifyPerson(user.id)
assert(result)
}
Example solution in playground
import org.junit.Assert.assertThrows
import org.junit.Test
import java.lang.AssertionError
import java.lang.IllegalStateException
import kotlin.test.assertEquals
fun Notifier.notifyUser(user: User?) {
user ?: return
// or
// if(user == null) return
if(!checkId(user.id)) throw IncorrectId()
require(user.name != null) {
"Name cannot be null"
}
require(user.surname != null) {
"Surname cannot be null"
}
check(initialized) {
"Notifier is not initialized"
}
val result = notifyPerson(user.id)
assert(result)
}
data class User(
val id: Int,
val name: String?,
var surname: String?
)
class IncorrectId : Error()
interface Notifier {
/**
* Indicate instance readiness to notify users
*/
val initialized: Boolean
/**
* Notifies person
* @param id Is an id of user we want to notify
* @return Was the operation successful
*/
fun notifyPerson(id: Int): Boolean
/**
* Checks if we can send message to the following id
*/
fun checkId(id: Int): Boolean
}
class RequirementsChecks {
@Test
fun `Function sends message for correct arguments and state`() {
val notifier = FakeNotifier(initialized = true)
val id = 123
notifier.notifyUser(User(id, "Ben", "Barack"))
assertEquals(setOf(id), notifier.usersNotified)
}
@Test
fun `Function does nothing when user is null`() {
val notifier = FakeNotifier(initialized = true)
notifier.notifyUser(null)
assertEquals(setOf(), notifier.usersNotified)
}
@Test
fun `Function throws IllegalArgumentException when name is null`() {
val notifier = FakeNotifier(initialized = true)
val id = 123
assertThrows(IllegalArgumentException::class.java) { notifier.notifyUser(User(id, null, "Kowalski")) }
}
@Test
fun `Function throws IllegalArgumentException when surname is null`() {
val notifier = FakeNotifier(initialized = true)
val id = 123
assertThrows(IllegalArgumentException::class.java) { notifier.notifyUser(User(id, "Barack", null)) }
}
@Test
fun `Function throws IllegalStateException when notifier is not initialized`() {
val notifier = FakeNotifier(initialized = false)
val id = 123
assertThrows(IllegalStateException::class.java) { notifier.notifyUser(User(id, "Mike", "Bull")) }
}
@Test
fun `Function throws IncorrectId when id is incorrect`() {
val notifier = FakeNotifier(initialized = true)
assertThrows(IncorrectId::class.java) { notifier.notifyUser(User(INCORRECT_ID, "Mike", "Bull")) }
}
@Test
fun `It is expected that notifyPerson will return true to indicate success`() {
val notifier = FakeNotifier(initialized = true)
assertThrows(IncorrectId::class.java) { notifier.notifyUser(User(INCORRECT_ID, "Mike", "Bull")) }
}
@Test
fun `Function should check if notifyPerson returns true as expected in correct conditions`() {
val notifier = FakeNotifier(initialized = true)
val id = 123
notifier.incorrectImplementationMakingNotifyPersonReturnFalse = true
assertThrows(AssertionError::class.java) { notifier.notifyUser(User(id, "Ben", "Barack")) }
}
class FakeNotifier(initialized: Boolean = false): Notifier {
override var initialized = initialized
private set
var usersNotified = setOf<Int>()
var incorrectImplementationMakingNotifyPersonReturnFalse = false
override fun checkId(id: Int): Boolean = id != INCORRECT_ID
override fun notifyPerson(id: Int): Boolean {
if(incorrectImplementationMakingNotifyPersonReturnFalse) return false
usersNotified = usersNotified + id
return true
}
}
companion object {
const val INCORRECT_ID = -100
}
}
