Unable to extract commonMain resources in commonTest when running android unit tests in KMM app (missing JVM resource generation for androidTest?).

[darronschall]

Hello!

I'm using moko-mvvm in a KMM app to share common view model business logic between my Android and iOS app. I'm also using moko-resources.

I'm able to use my commonMain/resources in my Android and iOS UI code without issue, e.g.:

// Example resource usage in SwiftUI
Button(MR.strings().example_button_label_resource_string.desc().localized())

// Example resource usage in ComposeUI
Text(text = stringResource(id = MR.example_button_label_resource_string.resourceId))

The problem I'm having is that I would like to use a resource string in my viewModel. There is no helper for this out-of-the-box, so I created a platform wrapper, like this:

// in `commonMain`
interface Resources {
    fun string(stringResource: StringResource): String
    // TODO: More helpers here for substitutions, plurals, etc.
}

// in `iosMain`
class IosResources : Resources {
    override fun string(stringResource: StringResource): String {
        return stringResource.desc().localized()
    }
}

// in `androidMain`
class AndroidResources(
    private val context: Context
) : Resources {
    override fun string(stringResource: StringResource): String {
        return stringResource.desc().toString(context)
    }
}

I can then provide this wrapper to my view model. This lets me go through the Resources interface to extract a resource string that the viewModel can bind to.

For example, given this resource (in commonMain/resources/MR/base):

<?xml version="1.0" encoding="UTF-8" ?>
<resources>
    <string name="example_error">Demo error message.</string>
</resources>

I can use my Resources interface to get the value at runtime in my view model:

// Supply `resources` via class constructor; e.g. `get()` from Koin after adding platform-specific `Resources`
// implementation to object graph.
class ExampleViewModel(private val resources: Resources) : ViewModel() {
    // Sample value for display in the view
    private val _errorMessage: CMutableStateFlow<String> = MutableStateFlow("").cMutableStateFlow()
    val errorMessage: CStateFlow<String> = _errorMessage.cStateFlow()  

    fun demoError() {
        // Use `resources.string` to extract the string value matching the resource key
        _errorMessage.value = resources.string(MR.strings.example_error)
    }
}

This works great. When running my Android and iOS app, I can see the "Demo error message" string in the view.

The problem I'm having is in my view model test declared in commonTest. I'm unable to extract the resources because androidTest runs on the JVM as unit tests, and it doesn't look like moko-resources generates those resources.

class ExampleViewModelTest {
    // This is not a great test, but trying to set up the minimal structure to demonstrate the problem
    @Test
    fun `error message is properly set on failure`() = runTest {
        val resources = createResources()
        val viewModel = ExampleViewModel(resources)
        
        viewModel.demoError()
        
        assertEquals("Demo error message.", viewModel.errorMessage.value)
    }
}

I made a createResources test helper, so that when running the tests I can use the correct implementation for my Resources wrapper. This type of test passes when running iosSimulatorArm64Test (the resources are available and work fine), but fails when running testReleaseUnitTest because the JVM resources cannot be found.

Here's what createResources() looks like:

// in `commonTest`
expect fun createResources(): Resources

// in `iosTest`
actual fun createResources(): Resources {
    return IosResources()
}

// in `androidTest
actual fun createResources(): Resources {
    // Can't do this, because no Android context (no instrumentation)
    // return AndroidResources(no_context_available_in_unit_tests)

    // So, we have to take another approach....
    // Since this runs via the JVM, try to load JVM resource instead:
    return object : Resources {
         override fun string(stringResource: StringResource): String {
             val resourcesClassLoader: ClassLoader = ClassLoader.getSystemClassLoader()
             // !!! This doesn't work; there are no resources available. Maybe I have the wrong bundle?
             val resourceBundle = resourcesClassLoader.getResourceBundle("resources", Locale.getDefault())
             return resourceBundle.getString(stringResource.resourceId.toString())
         }
     }
}

// Helper copied from https://github.com/icerockdev/moko-resources/blob/a4759a4439a492b6b8a6f7fa631be7cf0bdbe248/resources/src/jvmMain/kotlin/dev/icerock/moko/resources/ClassLoaderExt.kt#L10
 fun ClassLoader.getResourceBundle(bundleName: String, locale: Locale): ResourceBundle {
     return ResourceBundle.getBundle(
         bundleName,
         locale,
         this,
         // Otherwise, the default locale will be picked from system settings
         ResourceBundle.Control.getNoFallbackControl(ResourceBundle.Control.FORMAT_DEFAULT)
     )
 }

I tried to have my androidTest resource loader take the same kind of approach that moko-resources jvmMain does, but it's still not quite right.

I also tried using the resources-test library, but the createStringResourceMock() does not help me pull the string value from the strings.xml file in my commonTest test.

In summary:

• How can I instruct moko-resources to generate JVM resources so that I can use them in androidTest? I don't want to add a JVM target to my project (it is iOS + Android only). This seems like a bug that can be solved with a plugin update?

  • Or, is there a different approach to androidTest that I can take other than the ones I've already tried?

• Related, would a future release of moko-resources be open to including the Resources interface and platform implementations, to make it easier to use resources in moko-mvvm view models like I demonstrated? I'm happy to submit a PR if others see value in it.