1. Create a new test class:

class MyTest {
}

2. Add a mocked Api type test-class property:

class MyTest {
    val api: Api = mock()
}

3. Instantiate the Authenticator class as the class property:

class MyTest {
    val api: Api = mock()
    val authenticator = Authenticator(api)
}

4. Implement the test to verify whether the Api.authorise() function is called at least 10 times in case of consecutive failed authorization attempts:

class MyTest {
    val api: Api = mock()
    val authenticator = Authenticator(api)

    @Test
    fun `should retry auth at least 10 times when Api returns empty
    token`() {
        whenever(api.authorise(any())) doReturn ""

        val context = TestCoroutineContext()

        runBlocking(context) {
          authenticator.tryToAuthorise("admin:1234".toByteArray(),
            context)
                   .await()
            context.advanceTimeBy(100, TimeUnit.SECONDS)
            verify(api, atLeast(10)).authorise(any())
        }
    }
}