How do you test code that uses ReentrantLock?

import java.util.concurrent.locks.ReentrantLock;

class SharedResource {
    private final ReentrantLock lock = new ReentrantLock();
    private int resource = 0;

    public void increment() {
        lock.lock();
        try {
            resource++;
        } finally {
            lock.unlock();
        }
    }

    public int getResource() {
        return resource;
    }
}

public class ReentrantLockTest {
    public static void main(String[] args) throws InterruptedException {
        SharedResource sharedResource = new SharedResource();
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                sharedResource.increment();
            }
        });

        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                sharedResource.increment();
            }
        });

        t1.start();
        t2.start();
        t1.join();
        t2.join();

        System.out.println("Final resource value: " + sharedResource.getResource());
    }
}