A simple implementation of a mock library

SimpleMockitoTest.kt

import net.sf.cglib.proxy.Enhancer
import net.sf.cglib.proxy.MethodInterceptor
import net.sf.cglib.proxy.MethodProxy
import org.hamcrest.core.Is.`is`
import org.junit.Assert.assertThat
import org.junit.Test
import java.lang.reflect.Method
import java.net.Socket

inline fun <reified T> createMock(interceptor: MethodInterceptor) = Enhancer().apply {
    setSuperclass(T::class.java)
    setCallback(interceptor)
}.create() as T

class SimpleMockitoTest {
    private val mockedSocket = createMock<Socket>(MethodInterceptor { thiz: Any, method: Method, args: Array<Any?>, methodProxy: MethodProxy ->
        when (method.name) {
            "getLocalPort" -> 42
            "getInputStream" -> "foo bar".byteInputStream()
            "setSoTimeout" -> assertThat(args[0] as Int, `is`(70))
            else -> throw UnsupportedOperationException(method.name)
        }
    })

    @Test
    fun testSocket() {
        assertThat(mockedSocket.localPort, `is`(42))
        assertThat(mockedSocket.getInputStream().bufferedReader().use { it.readText() }, `is`("foo bar"))
        mockedSocket.soTimeout = 70
    }
}