使用kotlinx协同程序测试中的类时出错

kotlinx-coroutines-test依赖项似乎对我不起作用，因为我无法访问TestCoroutineDispatcher、setMain()、resetMain()等依赖项的成员.我遵循这doc个，但尽管添加了gradle依赖项，也无法访问成员.我试图重建项目，使缓存失效，然后重新启动，但似乎什么都不起作用.我也试过做androidExtensions {experimental = true}，但还是没有成功.

build.gradle个

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

apply plugin: 'kotlin-kapt'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.android.kotlincoroutines"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}
androidExtensions {
    experimental = true
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.1.1'
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1'


    implementation 'androidx.appcompat:appcompat:1.1.0-alpha02'
    implementation 'com.google.android.material:material:1.1.0-alpha03'

    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

    // ViewModel and LiveData
    def lifecycle_version = '2.0.0-beta01'
    implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0-alpha02"
    testImplementation "androidx.arch.core:core-testing:$lifecycle_version"

    // Room for database
    def room_version = '2.0.0'
    implementation "androidx.room:room-runtime:$room_version"
    kapt "androidx.room:room-compiler:$room_version"

    def work_version = "1.0.0-rc01"
    implementation "android.arch.work:work-runtime:$work_version"

    androidTestImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.1'
    androidTestImplementation 'androidx.test:rules:1.1.1'
    androidTestImplementation "com.google.truth:truth:0.42"
    androidTestImplementation "androidx.arch.core:core-testing:$lifecycle_version"

    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.0-M1'
}

Where am I going wrong here?