Exercise: Specify expectations
Implement the notifyUser function that notifies the user using notifier unless:
- The
userproperty isnull, in which case do nothing. - The
idproperty is incorrect according to thecheckIdfunction from Notifier, in which case throw anIncorrectIdexception. user.nameoruser.surnameisnull, in which case you should throwIllegalArgumentException.- The notifier is not initialized, which is an incorrect state, in which case you should throw
IllegalStateException. notifyPersondoes not returntruewhen you send a notification, in which case throwAssertionError.
Starting code:
fun Notifier.notifyUser(user: User?) {
TODO()
}
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
}
This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in effective/safe/NotifyUser.kt. You can find there starting code and unit tests.
Once you are done with the exercise, you can check your solution here.
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?) {
TODO()
}
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
}
}
