void methods

Mockito’s when method doesn’t work with void methods. To create a stub that doesn’t return anything, the doNothing method is used.

val mockedFile = mock(File::class.java)
doNothing().`when`(mockedFile).write(any())

MockK doesn’t have any restrictions with these methods, as they return Unit in Kotlin. As a result, the standard returns infix function can be used.

val mockedFile = mockk<File>()
every { mockedFile.write(any()) } returns Unit

MockK also provides the justRun method as a shorthand for every { x } returns Unit. For more information, see the Returning Unit tip.

val mockedFile = mockk<File>()
justRun { mockedFile.write(any()) }