JAVA-17333 Update Java Timer Article (#13423)

* JAVA-17333 Update Java Timer Article

* JAVA-17333 Rename the test class

---------

Co-authored-by: timis1 <noreplay@yahoo.com>

core-java-modules/core-java-time-measurements/src/main/java/com/baeldung/timer/NewsletterTask.java

@@ -3,12 +3,24 @@ package com.baeldung.timer;
 import java.time.Instant;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
+import java.util.Random;
 import java.util.TimerTask;
+import java.util.concurrent.TimeUnit;
 
 public class NewsletterTask extends TimerTask {
     @Override
     public void run() {
         System.out.println("Email sent at: "
           + LocalDateTime.ofInstant(Instant.ofEpochMilli(scheduledExecutionTime()), ZoneId.systemDefault()));
+        Random random = new Random();
+        int value = random.ints(1, 7)
+                .findFirst()
+                .getAsInt();
+        System.out.println("The duration of sending the mail will took: " + value);
+        try {
+            TimeUnit.SECONDS.sleep(value);
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
     }
 }

core-java-modules/core-java-time-measurements/src/test/java/com/baeldung/timer/NewsletterTaskUnitManualTest.java

@@ -5,7 +5,7 @@ import org.junit.jupiter.api.Test;
 
 import java.util.Timer;
 
-class NewsletterTaskUnitTest {
+class NewsletterTaskUnitManualTest {
     private final Timer timer = new Timer();
 
     @AfterEach
@@ -17,17 +17,13 @@ class NewsletterTaskUnitTest {
     void givenNewsletterTask_whenTimerScheduledEachSecondFixedDelay_thenNewsletterSentEachSecond() throws Exception {
         timer.schedule(new NewsletterTask(), 0, 1000);
 
-        for (int i = 0; i < 3; i++) {
-            Thread.sleep(1000);
-        }
+        Thread.sleep(20000);
     }
 
     @Test
     void givenNewsletterTask_whenTimerScheduledEachSecondFixedRate_thenNewsletterSentEachSecond() throws Exception {
         timer.scheduleAtFixedRate(new NewsletterTask(), 0, 1000);
 
-        for (int i = 0; i < 3; i++) {
-            Thread.sleep(1000);
-        }
+        Thread.sleep(20000);
     }
 }