I wanted to re-implement `InstancePerLeaf` as an e...

# kotest

[Lukasz Kalnik]

I wanted to re-implement InstancePerLeaf as an extension/listener. Do you have any hints how I could go about it? More details in 🧵

[Lukasz Kalnik]

We are testing viewmodels. Viewmodels are essentially state machines. Not all state transitions are allowed.

[Lukasz Kalnik]

E.g. we have cases where the viewmodel should emit state where it shows a dialog. Then there should be two child tests, "dialog confirmed" and "dialog dismissed". Then every of these cases can also have child tests etc.

[Lukasz Kalnik]

The point is, every one of the resulting leaf tests should be completely independent of "parallel" leaf tests (siblings). But should take into account the whole ancestry path that leads to the leaf tests, i.e. all surrounding container tests.

[Lukasz Kalnik]

That means at the last container test I have to somehow cache the state of system-under-test (the viewmodel) and then pass it to initialize every final leaf test. However, I also have to do it at every surrounding container test level, and recursively until the first container test.
I could omit the caching for the container tests which only contain one child.

[Lukasz Kalnik]

Example test

"given a viewmodel was created" - {
    val viewModel = MyViewModel()
    viewModel.uiState shouldBe EmptyState

    "when the customer scanned the wrong code then show error dialog" - {
        viewModel.scanCode(wrongCode)
        viewModel.uiState shouldBe ErrorDialog

        "when the customer dismissed the dialog then close it" {
            viewModel.onDismissErrorDialog()
            viewModel.uiState shouldBe EmptyState
        }

        "when customer selected manual input then show manual input dialog" - {
            viewModel.onManualInputSelected()
            viewModel.uiState shouldBe ManualInput

            "when the customer entered correct code manually then show success" {
                viewModel.enterCode(correctCode)
                viewModel.uiState shouldBe Success
            }
        }
    }

    "when the customer scanned the correct code then show success" {
        viewModel.scanCode(correctCode)
        viewModel.uiState shouldBe Success
    }
}

[Lukasz Kalnik]

The point is, e.g. calling scanCode() in Success state should not be allowed.

[Lukasz Kalnik]

Or calling onManualInputSelected() should also only be allowed in ErrorDialog state, not in EmptyState.

[Lukasz Kalnik]

So you cannot just run the tests through from top to bottom, keeping the old state. The state has to be reset to the level of the containing test, before entering next child test.

[Lukasz Kalnik]

So I think the solution would be:
1. At the end of every container test cache the system-under-test (viewmodel)
2. inject it at the beginning of the contained test

[Lukasz Kalnik]

For this I need to know exactly at which node of the test tree I currently am.
I.e. for this structure:

class MyTest : FreeSpec({
    
    "a" - {
        sut.doSomething()

        "b" - {
             sut.doSomethingElse()

            "c" {
                sut.doSomethingMore()
            }

            "d" {
                sut.doSomething()
            } 
        }

        "e" {
            sut.doSomethingElseYet()
        }
    }
})

I need to inject sut in state from the end of "a" to "b" and "e".
I need to inject sut in the state from the end of "b" to "c" and "d".

[Lukasz Kalnik]

So I need a map of unambiguous container test node coordinates to sut instances.
And I need to know which test node's child the current test is (what its container is).

[Lukasz Kalnik]

Note for simplicity that we don't allow code to be executed between siblings (e.g. "c" and "d" or "b" and "e").

[Lukasz Kalnik]

Is there a Listener/Extension which gives access to the current & containing test coordinates?

[Lukasz Kalnik]

Or would something like this have to be implemented deeply in the framework itself?

[Lukasz Kalnik]

Also I need a way to reference the injected sut somehow in the test body.