Testing flow combine

I'm trying to write some tests for my flow (that I know works by testing it manually), but the unit tests won't work.

I have this view model:

class TestViewModel(
    customerRepository: CustomerRepository,
): ViewModel() {
    private val phoneNumber = MutableStateFlow(customerRepository.getCustomer().phoneNumber)
    private val email = MutableStateFlow(customerRepository.getCustomer().email)

    val state: StateFlow<TestContactInformationState> = combine(
        phoneNumber,
        email,
    ) { phoneNumber, email ->
        TestContactInformationState(
            phoneNumber = phoneNumber,
            email = email,
        )
    }.stateIn(
        viewModelScope,
        SharingStarted.WhileSubscribed(),
        TestContactInformationState(
            customerRepository.getCustomer().phoneNumber,
            customerRepository.getCustomer().email,
        ),
    )

    fun setPhoneNumber(newPhoneNumber: PhoneNumber?) {
        this.phoneNumber.value = newPhoneNumber
    }

    fun setEmail(newEmail: Email?) {
        this.email.value = newEmail
    }
}

data class TestContactInformationState(
    val phoneNumber: PhoneNumber?,
    val email: Email?,
)

And I have this test:

@Test
fun `testing stuff`() = runTest {
    val customer = FakeCustomerRepository.fakeCustomer.copy(
        phoneNumber = "+46701234567".toPhoneNumber(),
        email = "hello@mail.com".toEmail(),
    )

    val stateHolder = TestViewModel(
        customerRepository = FakeCustomerRepository(
            fakeCustomer = customer,
        ),
    )

    stateHolder.setPhoneNumber("+46701234568".toPhoneNumber())
    stateHolder.setEmail("fs@sefs.se".toEmail())

    assertEquals("+46701234568".toPhoneNumber(), stateHolder.state.value.phoneNumber)
}

However it fails with this message:

Expected:<+46701234568> but was:<+46701234567>
Expected :+46701234568
Actual   :+46701234567

I have also tried with adding advanceUntilIdle() but that doesn't make any difference

Flows need to be observed.

You are checking the value directly in this line

stateHolder.state.value.phoneNumber

Instead, you should do something like this:

stateHolder.state.first()

Notice how first() is a suspend function, therefore it needs to be called within your runTest{} block.
first() is fetching the first emission of your flow. There are other options useful in tests, such as .toList() to fetch several emissions of a flow.

In production code you wouldn't use any of this, simply observe the flow or collect it.