Exercise: Mocking library
Your task is to implement a simple library for interface mocking. You should only support mocking interface methods that do not throw exceptions. This is how you should use it:
data class User(val name: String)
interface UserRepository {
fun getUser(userId: String): User?
fun allUsers(): List<User>
}
interface UserService {
fun getUser(): User
}
fun main() {
val registry = MockRegistry()
val userRepository = registry.mock<UserRepository>()
val userService = registry.mock<UserService>()
registry.setReturnValue(
{ userRepository.getUser("alex") },
User("Alex Smith")
)
registry.setReturnValue(
{ userRepository.getUser("bell") },
User("Bell Rogers")
)
registry.setReturnValue(
{ userRepository.getUser("dan") },
null
)
registry.setBody({ userRepository.allUsers() }) {
listOf(User("James Bond"), User("Jane Doe"))
}
registry.setBody({ userService.getUser() }) {
User(userRepository.getUser("dan")?.name ?: "Unknown")
}
println(userRepository.getUser("alex"))
// User(name=Alex Smith)
println(userRepository.allUsers())
// [User(name=James Bond), User(name=Jane Doe)]
println(userRepository.getUser("bell"))
// User(name=Bell Rogers)
println(userService.getUser())
// User(name=Unknown)
registry.setReturnValue(
{ userRepository.getUser("dan") },
User("Dan Brown")
)
println(userService.getUser())
// User(name=Dan Brown)
}
Your implementation should use Proxy from the java.lang.reflect package.
You can find unit tests and usage examples in the MarcinMoskala/kotlin-exercises project on GitHub in the file advanced/java/Mocking.kt. You can clone this project and solve this exercise locally.
Hints:
- A mocked method can be called to both record and use the mock. To know what situation it is, define a
recordingflag in your class. - Each call is identified by three things: mock object identifier, method name, and method arguments. You can define a data class to keep those three things.
Once you are done with the exercise, you can check your solution here.
