MockitoTests.kt

import org.hamcrest.MatcherAssert
import org.hamcrest.Matchers
import org.junit.Before
import org.junit.Test
import org.mockito.InjectMocks
import org.mockito.Mock
import org.mockito.Mockito
import org.mockito.MockitoAnnotations
import javax.inject.Inject
import javax.servlet.http.HttpServletRequest


interface Database {
    fun findUser(): User

}
class User(val name:String)
class MyComponent {

    @Inject private lateinit var request: HttpServletRequest
    @Inject private lateinit var database: Database

    val user: User by lazy {
        database.findUser()
    }

    fun getUsername(): String {
        return user.name
    }
}

class MyComponentTest {

    @Mock private lateinit var request: HttpServletRequest
    @Mock private lateinit var database: Database

    @InjectMocks private lateinit var sut: MyComponent

    @Before
    fun setup() {
        MockitoAnnotations.initMocks(this)
    }

    @Test
    fun `username`() {
        Mockito.`when`(database.findUser()).thenReturn(User("test"))
        val username = sut.getUsername()

        MatcherAssert.assertThat(username, Matchers.equalTo("test"))
    }
}