faking.kt

import java.lang.reflect.Proxy

inline fun <reified T> fake(): T =
    Proxy.newProxyInstance(
        T::class.java.classLoader,
        arrayOf(T::class.java)
    ) { _, _, _ ->
        TODO("not implemented")
    } as T


val sentEmails = mutableListOf<Email>()
val testCollaborator: EmailSystem =
    object : EmailSystem by fake() {
        override fun send(email: Email) {
            sentEmails.add(email)
        }
    }