IssueTracker

Ah sorry I forgot versions

Kotlin - 1.6.10
Gradle - 7.4
AGP    - 7.2.0-beta02

And super thank you for making it happening!

The other issue also tracks kotlin support, also take a look at https://youtrack.jetbrains.com/issue/KT-50667

YouTrack issue is closed as "Third Party", ball is back at Google's side.

Duplicate this against https://issuetracker.google.com/issues/259523353 ?

I was able to find a solution, not sure if every step is required but this is what worked for me.

Tested working with: AGP: 8.7.2, Gradle: 8.9, Kotlin: 2.0.0 / 2.0.20

Does not work with: AGP: 8.4.2, Gradle: 8.7 : Error - IDE Linter can find the class, no syntax highlight errors, but get Unresolved Reference upon execution.

Procedure

1. It's not necessary to convert classes Java.
2. Move your testFixtures directory to your :app module
3. Modify the package name to match whatever you have in android.namespace (not sure if this is required)
4. Add a sourceSet to :app/build.gradle.kts

    sourceSets {
     ...
        getByName("testFixtures") {
            java.srcDir("src/testFixtures/java") //my files are in the java folder
            resources.srcDir("src/testFixtures/resources")
        }
   

5. Remove the plugin id(java-test-fixtures) (everywhere)
6. In the build.gradle.kts of the implementing module use:
   testImplementation(testFixtures(projects.app)) or testImplementation(testFixtures(project(":app")) // Counter to intuition you won't create a circular reference.
7. You need to declare testFixturesImplementation dependencies in :app/build.gradle.kts.

• My project never asked for it before but required kotlin runtime and compose runtime on the classpath.
• It also required me to add composeOptions which I never had before

Now my :app/build.gradle.kts additions look like this

android {
   ...
  composeOptions {
        kotlinCompilerExtensionVersion = "1.5.15"
    }
   ... 
   sourceSets {
   ...
    getByName("testFixtures") {
            java.srcDir("src/testFixtures/java")
            resources.srcDir("src/testFixtures/resources")
        }
   ...
   }
}
...
dependencies {
   ...
    implementation(libs.androidx.compose.runtime) //new 

    testFixturesImplementation(libs.junit)
    testFixturesImplementation(libs.androidx.test.core)
    testFixturesImplementation(libs.androidx.test.runner)
    testFixturesImplementation(libs.androidx.junit.core.ktx)
    testFixturesImplementation(libs.androidx.arch.core.testing)
    testFixturesImplementation(libs.timber)

    testFixturesCompileOnly(libs.kotlin.stdlib) // I believe this is required
    testFixturesRuntimeOnly(libs.kotlin.stdlib) // I believe this is required
    testFixturesImplementation(libs.androidx.compose.runtime)
    ...
}

I also have this in gradle.properties

android.experimental.enableTestFixtures=true
android.experimental.enableTestFixturesKotlinSupport=true

More info:

For example: Say we want to access the proper objects in :domain/SomeTest.kt in order to successfully execute this line:

val fakeItem = json.decodeFromString<ItemEntity>(loadJsonFromResources("fakeitementity.json")).toDomain()

where .toDomain() and ItemEntity is from data module, and fakeitementity.json is located in the :app module: project/app/src/testFixtures/resources

In order to share the app, domain, and data test fixtures will need this in :app/build.gradle.kts

testImplementation(projects.domain)
testImplementation(projects.data)
testFixturesImplementation(projects.domain)
testFixturesImplementation(projects.data)

To use them in the domain tests, you will need to add the module and its testFixtures in the :domain/build.gradle.kts

testImplementation(projects.domain)
testImplementation(projects.data)
testImplementation(testFixtures(projects.app))
testImplementation(testFixtures(projects.domain))

clean/build the app and wait for success!