BAEL-861 Introduction to Awaitlity (#2150)

* BAEL-748 quick guide to @Value

* BAEL-748 changes from review

* BAEL-748 inject comma-separated values into array

* BAEL-768 Introduction to Netty

* BAEL-768 remove commented code

* BAEL-861 Introduction to Awaitility

* BAEL-861 rename Test to UnitTest

libraries/src/main/java/com/baeldung/awaitility/AsyncService.java

@@ -0,0 +1,50 @@
+package com.baeldung.awaitility;
+
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class AsyncService {
+    private final int DELAY = 1000;
+    private final int INIT_DELAY = 2000;
+
+    private AtomicLong value = new AtomicLong(0);
+    private Executor executor = Executors.newFixedThreadPool(4);
+    private volatile boolean initialized = false;
+
+    public void initialize() {
+        executor.execute(() -> {
+            sleep(INIT_DELAY);
+            initialized = true;
+        });
+    }
+
+    public boolean isInitialized() {
+        return initialized;
+    }
+
+    public void addValue(long val) {
+        if (!isInitialized()) {
+            throw new IllegalStateException("Service is not initialized");
+        }
+        executor.execute(() -> {
+            sleep(DELAY);
+            value.addAndGet(val);
+        });
+    }
+
+    public long getValue() {
+        if (!isInitialized()) {
+            throw new IllegalStateException("Service is not initialized");
+        }
+        return value.longValue();
+    }
+
+    private void sleep(int delay) {
+        try {
+            Thread.sleep(delay);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+}