diff --git a/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/AsynchronousCallbackUnitTest.java b/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/AsynchronousCallbackUnitTest.java
index 494d7365d3..de9e386395 100644
--- a/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/AsynchronousCallbackUnitTest.java
+++ b/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/AsynchronousCallbackUnitTest.java
@@ -6,8 +6,7 @@ import com.baeldung.callbackfunctions.EventListener;
 import com.baeldung.callbackfunctions.asynchronous.AsynchronousEventConsumer;
 import com.baeldung.callbackfunctions.asynchronous.AsynchronousEventListenerImpl;
 
-import static org.mockito.Mockito.times;
-import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.*;
 
 public class AsynchronousCallbackUnitTest {
 
@@ -17,6 +16,6 @@ public class AsynchronousCallbackUnitTest {
         AsynchronousEventConsumer asynchronousEventListenerConsumer = new AsynchronousEventConsumer(listener);
         asynchronousEventListenerConsumer.doAsynchronousOperation();
 
-        verify(listener, times(1)).onTrigger();
+        verify(listener, timeout(1000).times(1)).onTrigger();
     }
 }
diff --git a/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/ConsumerCallbackUnitTest.java b/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/ConsumerCallbackUnitTest.java
index ba09a7e50c..9ba5cdb6ef 100644
--- a/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/ConsumerCallbackUnitTest.java
+++ b/core-java-modules/core-java-functional/src/test/java/com/baeldung/callbackfunctions/ConsumerCallbackUnitTest.java
@@ -3,18 +3,25 @@ package com.baeldung.callbackfunctions;
 import org.junit.jupiter.api.Test;
 import com.baeldung.callbackfunctions.ConsumerCallback;
 
+import java.util.concurrent.atomic.AtomicInteger;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class ConsumerCallbackUnitTest {
 
     @Test
-    public void whenIncreasingInitialAgeByGivenValueThroughCallback_shouldIncreaseAge(){
+    void whenIncreasingInitialAgeByGivenValueThroughCallback_shouldIncreaseAge(){
         ConsumerCallback consumerCallback = new ConsumerCallback();
-        consumerCallback.getAge(20, (initialAge) -> {
-            int ageDifference = 10;
+        int ageDifference = 10;
+        AtomicInteger newAge1 = new AtomicInteger();
+        int initialAge = 20;
+        consumerCallback.getAge(initialAge, (initialAge1) -> {
             consumerCallback.increaseAge(initialAge, ageDifference, (newAge) -> {
-                assertEquals(initialAge + ageDifference, newAge);
+                System.out.printf("New age ==> %s", newAge);
+                newAge1.set(newAge);
+
             });
         });
+        assertEquals(initialAge + ageDifference, newAge1.get());
     }
 }