Kotlin Multiplatform test resources

build.gradle

// Part of a multi-module project, hence the rootProject everywhere
task copyTestResourcesForJs(type: Copy) {
    from "$projectDir/src/commonTest/resources"
    into "${rootProject.buildDir}/js/packages/${rootProject.name}-${project.name}-test/src/commonTest/resources"
}

jsNodeTest.dependsOn copyTestResourcesForJs

Resource.kt

// Common
const val RESOURCE_PATH = "./src/commonTest/resources"

expect class Resource(name: String) {
    val name: String

    fun exists(): Boolean
    fun readText(): String
}

// JVM
import java.io.File

actual class Resource actual constructor(actual val name: String) {
    private val file = File("$RESOURCE_PATH/$name")

    actual fun exists(): Boolean = file.exists()

    actual fun readText(): String = file.readText()
}

// Native
import kotlinx.cinterop.*
import platform.posix.*

actual class Resource actual constructor(actual val name: String) {
    private val file: CPointer<FILE>? = fopen("$RESOURCE_PATH/$name", "r")

    actual fun exists(): Boolean = file != null

    actual fun readText(): String {
        fseek(file, 0, SEEK_END)
        val size = ftell(file)
        rewind(file)

        return memScoped {
            val tmp = allocArray<ByteVar>(size)
            fread(tmp, sizeOf<ByteVar>().convert(), size.convert(), file)
            tmp.toKString()
        }
    }
}

// JS (Node)
private external fun require(module: String): dynamic
private val fs = require("fs")

actual class Resource actual constructor(actual val name: String) {
    private val path = "$RESOURCE_PATH/$name"

    actual fun exists(): Boolean = fs.existsSync(path) as Boolean

    actual fun readText(): String = fs.readFileSync(path, "utf8") as String
}

Usage.kt

@Test
fun testLength2() {
    // Located at /src/commonTest/resources/test.json
    val resource = Resource("test.json")
    val geometry = resource.readText().toGeometry<LineString>()

    assertEquals(42.560767589197006, length(geometry, Units.Kilometers))
}

I haven't had a need to stream the input yet so I haven't really thought much about it, but you could probably use something like Okio and return an implementation of a Source (or whatever implementation of an InputStream you want to use). You'd just have to adjust the fread call to read the number of bytes that are requested.

Yesterday I played with this script a bit and it didn't really work for iosX64 target. I guess it's more complicated than that, after all it's not run inside an ios filesystem (although on an m1 mac there should be a way).

That's true. This was built for use in JVM, Native (non-iOS/watchOS/tvOS), and Node environments.

Android Instrumentation tests, those other Apple environments, and Browser environments would require some more work, but I suspect they're not impossible.

It didn't work for me while trying to run tests on iOS. This modification did the job:

// Native
import kotlinx.cinterop.*
import platform.posix.*

actual class Resource actual constructor(actual val name: String) {
    private val path = NSBundle.mainBundle.pathForResource("resources/FILE_NAME", "FILE_EXTENSION") ?: ""
    private val file: CPointer<FILE>? = fopen(path, "r")

Then, in the build.gradle.kts file:

tasks.register<Copy>("copyiOSTestResources") {
  from("src/commonTest/resources")
  into("build/bin/iosX64/debugTest/resources")
}

tasks.findByName("iosX64Test")!!.dependsOn("copyiOSTestResources")

This article helped me out a lot: https://developer.squareup.com/blog/kotlin-multiplatform-shared-test-resources/

Cannot you simply specify

private val path = "kotlin/$name"

in the JS implementation of the Resource class's constructor (i.e. without the need for the copyTestResourcesForJs Gradle task)?