BAEL-4472- Binary Semaphore vs a ReentrantLock - Unit test added

core-java-modules/core-java-concurrency-advanced-3/src/test/java/com/baeldung/binarysemaphorereentrantlock/BinarySemaphoreVsReentrantLockUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.binarysemaphorereentrantlock;
+
+import static org.junit.Assert.assertEquals;
+import java.util.concurrent.Semaphore;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.junit.Test;
+
+public class BinarySemaphoreVsReentrantLockUnitTest {
+
+    @Test
+    public void givenBinarySemaphore_whenAcquireAndRelease_thenCheckAvailablePermits() throws InterruptedException {
+        Semaphore binarySemaphore = new Semaphore(1); 
+        try { 
+            binarySemaphore.acquire(); 
+            assertEquals(0, binarySemaphore.availablePermits());
+        } catch (InterruptedException e) { 
+            e.printStackTrace(); 
+        } finally { 
+            binarySemaphore.release(); 
+            assertEquals(1, binarySemaphore.availablePermits()); 
+        }
+    }
+
+    @Test
+    public void givenReentrantLock_whenLockAndUnlock_thenCheckHoldCountAndIsLocked() throws InterruptedException {
+        ReentrantLock reentrantLock = new ReentrantLock(); 
+        try { 
+            reentrantLock.lock(); 
+            assertEquals(1, reentrantLock.getHoldCount()); 
+            assertEquals(true, reentrantLock.isLocked()); 
+        } finally { 
+            reentrantLock.unlock(); 
+            assertEquals(0, reentrantLock.getHoldCount()); 
+            assertEquals(false, reentrantLock.isLocked());
+        }
+    }
+    
+    @Test
+    public void givenReentrantLock_whenLockMultipleTimes_thenUnlockMultipleTimesToRelease() throws InterruptedException {
+        ReentrantLock reentrantLock = new ReentrantLock(); 
+        try { 
+            reentrantLock.lock(); 
+            reentrantLock.lock();
+            assertEquals(2, reentrantLock.getHoldCount()); 
+            assertEquals(true, reentrantLock.isLocked()); 
+        } finally { 
+            reentrantLock.unlock(); 
+            assertEquals(1, reentrantLock.getHoldCount()); 
+            assertEquals(true, reentrantLock.isLocked());
+            
+            reentrantLock.unlock(); 
+            assertEquals(0, reentrantLock.getHoldCount()); 
+            assertEquals(false, reentrantLock.isLocked());
+        }
+    }
+    
+}