Added unit test for Thread.join method

core-java/src/test/java/com/baeldung/thread/join/ThreadJoinUnitTest.java

@@ -0,0 +1,95 @@
+package com.baeldung.thread.join;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.logging.Logger;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+/**
+ * Demonstrates Thread.join behavior.
+ *
+ */
+public class ThreadJoinUnitTest {
+
+    final static Logger LOGGER = Logger.getLogger(ThreadJoinUnitTest.class.getName());
+
+    class SampleThread extends Thread {
+        public int processingCount = 0;
+
+        SampleThread(int processingCount) {
+            this.processingCount = processingCount;
+            LOGGER.info("Thread " + this.getName() + " created");
+        }
+
+        @Override
+        public void run() {
+            LOGGER.info("Thread " + this.getName() + " started");
+            while (processingCount > 0) {
+                try {
+                    Thread.sleep(1000); // Simulate some work being done by thread
+                } catch (InterruptedException e) {
+                    LOGGER.info("Thread " + this.getName() + " interrupted.");
+                }
+                processingCount--;
+                LOGGER.info("Inside Thread " + this.getName() + ", processingCount = " + processingCount);
+            }
+            LOGGER.info("Thread " + this.getName() + " exiting");
+        }
+    }
+
+    @Test
+    public void givenNewThread_whenJoinCalled_returnsImmediately() throws InterruptedException {
+        Thread t1 = new SampleThread(0);
+        LOGGER.info("Invoking join.");
+        t1.join();
+        LOGGER.info("Returned from join");
+        LOGGER.info("Thread state is" + t1.getState());
+        assertFalse(t1.isAlive());
+    }
+
+    @Test
+    public void givenStartedThread_whenJoinCalled_waitsTillCompletion() 
+      throws InterruptedException {
+        Thread t2 = new SampleThread(1);
+        t2.start();
+        LOGGER.info("Invoking join.");
+        t2.join();
+        LOGGER.info("Returned from join");
+        assertFalse(t2.isAlive());
+    }
+
+    @Test
+    public void givenStartedThread_whenTimedJoinCalled_waitsUntilTimedout() 
+      throws InterruptedException {
+        Thread t3 = new SampleThread(10);
+        t3.start();
+        t3.join(1000);
+        assertTrue(t3.isAlive());
+    }
+
+    @Test
+    @Ignore
+    public void givenThreadTerminated_checkForEffect_notGuaranteed() 
+      throws InterruptedException {
+        SampleThread t4 = new SampleThread(10);
+        t4.start();
+      //not guaranteed to stop even if t4 finishes.
+        do {
+            
+        } while (t4.processingCount > 0);  
+    }
+
+    @Test
+    public void givenJoinWithTerminatedThread_checkForEffect_guaranteed() 
+      throws InterruptedException {
+        SampleThread t4 = new SampleThread(10);
+        t4.start();
+        do {
+            t4.join(100);
+        } while (t4.processingCount > 0);
+    }
+
+}