Gradle(2.14) unable to pick useTestNG() method within SourceSets

I have a Java project with Gradle 2.1 and I want to upgrade the gradle version since the current version is too old. The below code works fine for gradle 2.13 and below. Here is the build.gradle file:

apply plugin: 'java'


repositories {
    mavenCentral()
}

sourceSets {
    test {
        useTestNG()
    }
}


dependencies {
    compile group: 'org.testng', name: 'testng', version: '6.9.10'
}

However I get the below message when I upgrade to gradle 2.14:

"Could not find method useTestNG() for arguments [] on source set 'test' of type org.gradle.api.internal.tasks.DefaultSourceSet."

If I define test{} block outside sourceSets the error goes away. Not sure why.