parallel-programming/src/test/java/MySemaphoreTest.java

import org.junit.jupiter.api.Test;
import ru.lionarius.sync.MySemaphore;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import static org.junit.jupiter.api.Assertions.*;

class MySemaphoreTest {
    @Test
    void testInitialization() {
        assertDoesNotThrow(() -> new MySemaphore(-1));
        assertDoesNotThrow(() -> new MySemaphore(0));
        var semaphore = new MySemaphore(5);
        assertEquals(5, semaphore.availablePermits());
    }

    @Test
    void testAcquireAndRelease() throws InterruptedException {
        var semaphore = new MySemaphore(2);
        assertEquals(2, semaphore.availablePermits());
        semaphore.acquire();
        assertEquals(1, semaphore.availablePermits());
        semaphore.acquire();
        assertEquals(0, semaphore.availablePermits());
        assertFalse(semaphore.tryAcquire());
        semaphore.release();
        assertEquals(1, semaphore.availablePermits());
        assertTrue(semaphore.tryAcquire());
        assertEquals(0, semaphore.availablePermits());
    }

    @Test
    void testTryAcquire() {
        var semaphore = new MySemaphore(2);
        assertTrue(semaphore.tryAcquire());
        assertEquals(1, semaphore.availablePermits());
        assertTrue(semaphore.tryAcquire());
        assertEquals(0, semaphore.availablePermits());
        assertFalse(semaphore.tryAcquire());
        assertEquals(0, semaphore.availablePermits());
    }

    @Test
    void testMultipleThreads() throws InterruptedException {
        final int THREAD_COUNT = 10;
        final int PERMITS = 3;
        
        var semaphore = new MySemaphore(PERMITS);
        
        var startLatch = new CountDownLatch(1);
        var finishLatch = new CountDownLatch(THREAD_COUNT);
        
        var concurrentThreads = new AtomicInteger(0);
        var maxConcurrentThreads = new AtomicInteger(0);

        for (int i = 0; i < THREAD_COUNT; i++) {
            new Thread(() -> {
                try {
                    startLatch.await();
                    semaphore.acquire();
                    
                    int current = concurrentThreads.incrementAndGet();
                    maxConcurrentThreads.updateAndGet(max -> Math.max(max, current));
                    
                    Thread.sleep(100);
                    
                    concurrentThreads.decrementAndGet();
                    
                    semaphore.release();
                    finishLatch.countDown();
                } catch (InterruptedException ignored) {
                }
            }).start();
        }

        startLatch.countDown();
        assertTrue(finishLatch.await(5, TimeUnit.SECONDS));
        assertEquals(PERMITS, maxConcurrentThreads.get());
        assertEquals(PERMITS, semaphore.availablePermits());
    }

    @Test
    void testBlockingAcquire() throws InterruptedException {
        var semaphore = new MySemaphore(1);
        semaphore.acquire();
        assertEquals(0, semaphore.availablePermits());
        
        var startLatch = new CountDownLatch(1);
        var doneLatch = new CountDownLatch(1);
        var thread = new Thread(() -> {
            try {
                startLatch.countDown();
                
                semaphore.acquire();
            } catch (InterruptedException ignored) {
            }

            doneLatch.countDown();
        });

        thread.start();
        startLatch.await();
        
        assertTrue(thread.isAlive());
        assertEquals(0, semaphore.availablePermits());

        semaphore.release();
        doneLatch.await();
        
        assertFalse(thread.isAlive());
        assertEquals(0, semaphore.availablePermits());
    }

    @Test
    void testAvailablePermits() {
        var semaphore = new MySemaphore(5);
        assertEquals(5, semaphore.availablePermits());
        semaphore.tryAcquire();
        assertEquals(4, semaphore.availablePermits());
        semaphore.release();
        assertEquals(5, semaphore.availablePermits());
    }
}