Parcelize testing

Movie.kt

import android.annotation.SuppressLint
import android.os.Parcelable
import kotlinx.android.parcel.Parcelize

@SuppressLint("ParcelCreator") // IntelliJ Issue https://youtrack.jetbrains.com/issue/KT-19300
@Parcelize
data class Movie(val title: String) : Parcelable

MovieTest.kt

import android.os.Parcel
import android.support.test.runner.AndroidJUnit4
import org.assertj.core.api.Assertions.assertThat
import org.junit.Test
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class MovieTest {

    @Test
    fun verify_parceling() {
        val movie = Movie("Infinity War")

        movie.testParcel()
                .apply {
                    assertThat(this).isEqualTo(movie)
                    assertThat(this).isNotSameAs(movie)
                }
    }
}

utils.kt

import android.os.Bundle
import android.os.Parcel
import android.os.Parcelable

inline fun <reified R : Parcelable> R.testParcel(): R {
    val bytes = marshallParcelable(this)
    return unmarshallParcelable(bytes)
}

inline fun <reified R : Parcelable> marshallParcelable(parcelable: R): ByteArray {
    val bundle = Bundle().apply { putParcelable(R::class.java.name, parcelable) }
    return marshall(bundle)
}

fun marshall(bundle: Bundle): ByteArray =
        Parcel.obtain().use {
            it.writeBundle(bundle)
            it.marshall()
        }

inline fun <reified R : Parcelable> unmarshallParcelable(bytes: ByteArray): R = unmarshall(bytes)
        .readBundle()
        .run {
            classLoader = R::class.java.classLoader
            getParcelable(R::class.java.name)
        }

fun unmarshall(bytes: ByteArray): Parcel =
        Parcel.obtain().apply {
            unmarshall(bytes, 0, bytes.size)
            setDataPosition(0)
        }

private fun <T> Parcel.use(block: (Parcel) -> T): T =
        try {
            block(this)
        } finally {
            this.recycle()
        }

I have a probe with unmarshallParcelable(), I get the following error:

Type mismatch.
Required: R
Found: Nothing?

How can I fix that?
Thanks.

Nothing? is a strange type to have. This type should not be serializable. Do you have in your parcel Nothing? type?

No I don't.
It happens in Android Studio when I copy/paste utils.kt in the test folder.
Does it only work in the androidTest folder, then?

It should work everywhere. The last time I've used the code was 2 years ago and kotlin changes most likely has changed it.
Could you include the whole stacktrace?

Again, that's all I have, no stack trace, it appears on Android Studio right after a copy/paste of that class.

Last thing, what kotlin version are you using?

1.6.21

The last last thing, is there a reason why you are not using https://developer.android.com/kotlin/parcelize ?
This solution was used before parcelize

I use parcelize, but I wanted to unit test a quite tricky use case, where one of the attribute of my parcelable object is of type Any, so I have to to the write(parcel: Parcel, flags: Int) and the create(parcel: Parcel) by myself.

Those two approaches do the same thing in a different way, therefore UT your prod code using this approach would actually not test the same functionality.
Did you consider using epresso tests for your current implementation?

I can only use pure unit test, since I'm working on a Flutter project (so there is no integration testing available, therefore I can't use Espresso).
But that's ok, I'll find another way, thanks.

I also work with flutter and you can write Espresso tests there. You can check out this link

Oh cool, I didn't know, thanks for the link!

The issue comes from getParcelable now correctly being annotated with @Nullable.
You can update the unmarshallParcelable return type to R? to fix this issue.