So now it's time to throw away our assumptions and write a mock DataSource that will retrieve from an external application faster than from the DB. Let's add another implementation of Datasource in the same SampleAppFT. We will call it MockSlowDbDataSource for lack of a better name:

// Mock a datasource that retrieves the data in a different order
class MockSlowDbDataSource: DataSource {
    // Mock getting the name from the database
    override fun getNameAsync(id: Int) = async {
        delay(1000)
        "Susan Calvin"
    }

    // Mock getting the age from the cache
    override fun getAgeAsync(id: Int) = async {
        delay(500)
        Calendar.getInstance().get(Calendar.YEAR) - 1982
    }

    // Mock getting the profession from an external system
    override fun getProfessionAsync(id: Int) = async {
        delay(200)
        "Robopsychologist"
    }
}

We will complete our second test using it:

@Test
fun testOppositeOrder() = runBlocking {
    val manager = UserManager(MockSlowDbDataSource())

    val user = manager.getUser(10)
    assertTrue { user.name == "Susan Calvin" }
    assertTrue { user.age == Calendar.getInstance().get(Calendar.YEAR) - 1982 }
    assertTrue { user.profession == "Robopsychologist" }
}

If we run this test, we will make the application crash: