How to run tests in a subproject structure

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I have subprojects X and Common, and while both compile just fine, the tests for X seem to fail at runtime because Common is not present, despite having tried to add it with runtime, testRuntime, testImplementation, etc.

root build.gradle:

plugins {
    id 'java'
    id 'org.jetbrains.kotlin.jvm' version "$kotlin_version"
    id "com.github.johnrengelman.shadow" version "$shadow_version"
}

group = 'com.martmists'
version = project_version
archivesBaseName = rootProject.name + "-all"

allprojects {
    apply plugin: 'java'
    apply plugin: 'kotlin'
    apply plugin: 'com.github.johnrengelman.shadow'

    project.version = rootProject.version
    project.group = rootProject.group
    project.setBuildDir(rootProject.getBuildDir())

    repositories {
        mavenCentral()
        maven {
            name = "Jitpack"
            url = "https://jitpack.io"
        }
    }

    configurations {
        // Make shade act as both implementation and testRuntime
        implementation.extendsFrom shade
        testRuntime.extendsFrom shade
    }

    jar {
        enabled = false
    }

    shadowJar {
        enabled = true
        configurations = [project.configurations.shade]
        classifier = ""
    }

    build.dependsOn(shadowJar)

    sourceCompatibility = JavaVersion.VERSION_16
    targetCompatibility = JavaVersion.VERSION_16
    compileKotlin.kotlinOptions.jvmTarget = "16"
    compileKotlin.kotlinOptions.useIR = true
    compileTestKotlin.kotlinOptions.jvmTarget = "16"
    compileTestKotlin.kotlinOptions.useIR = true
}

subprojects {
    archivesBaseName = rootProject.name + "-" + project.name
    rootProject.build.dependsOn(build)

    dependencies {
        implementation "org.jetbrains.kotlin:kotlin-stdlib"
        testImplementation 'org.junit.jupiter:junit-jupiter-api:5.4.2'
        testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.4.2'
    }

    test {
        useJUnitPlatform()
        include 'com/martmists/**'
    }
}

X build.gradle:

dependencies {
    shade project(path: ":common", configuration: "shadow")
    testRuntime project(path: ":common", configuration: "shadow")
}