EnumSetTearingTest.java

import java.util.EnumSet;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class EnumSetTearingTest {

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 100; i++) {
            EnumSet<TestEnum> set = EnumSet.noneOf(TestEnum.class);
            ExecutorService pool = Executors.newFixedThreadPool(4);
            for (TestEnum val : TestEnum.values()) {
                pool.submit(() -> {
                    set.add(val);
                });
            }
            pool.shutdown();
            pool.awaitTermination(1, TimeUnit.SECONDS);

            if (set.size() != TestEnum.values().length) {
                System.out.println("Boo!");
            } else {
                System.out.println("As expected");
            }

        }

    }

    public enum TestEnum {
        A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P;
    }
}