feat: Add Service Stub Pattern using Sentiment Analysis example (#3215)

* Add Service Stub Pattern using Sentiment Analysis example

* Fix Checkstyle issues

* Suppress Sonar warning for Random usage in RealSentimentAnalysisServer

service-stub/src/test/java/com/iluwatar/servicestub/AppTest.java

@@ -0,0 +1,11 @@
+package com.iluwatar.servicestub;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+public class AppTest {
+  @Test
+  void shouldExecuteWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[] {}));
+  }
+}

service-stub/src/test/java/com/iluwatar/servicestub/RealSentimentAnalysisServerTest.java

@@ -0,0 +1,26 @@
+package com.iluwatar.servicestub;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class RealSentimentAnalysisServerTest {
+
+  @Test
+  void testPositiveSentiment() {
+    RealSentimentAnalysisServer server = new RealSentimentAnalysisServer(() -> 0);
+    assertEquals("Positive", server.analyzeSentiment("Test"));
+  }
+
+  @Test
+  void testNegativeSentiment() {
+    RealSentimentAnalysisServer server = new RealSentimentAnalysisServer(() -> 1);
+    assertEquals("Negative", server.analyzeSentiment("Test"));
+  }
+
+  @Test
+  void testNeutralSentiment() {
+    RealSentimentAnalysisServer server = new RealSentimentAnalysisServer(() -> 2);
+    assertEquals("Neutral", server.analyzeSentiment("Test"));
+  }
+
+}

service-stub/src/test/java/com/iluwatar/servicestub/StubSentimentAnalysisServerTest.java

@@ -0,0 +1,27 @@
+package com.iluwatar.servicestub;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class StubSentimentAnalysisServerTest {
+
+  private final StubSentimentAnalysisServer stub = new StubSentimentAnalysisServer();
+
+  @Test
+  void testPositiveSentiment() {
+    String result = stub.analyzeSentiment("This is a good product");
+    assertEquals("Positive", result);
+  }
+
+  @Test
+  void testNegativeSentiment() {
+    String result = stub.analyzeSentiment("This is a bad product");
+    assertEquals("Negative", result);
+  }
+
+  @Test
+  void testNeutralSentiment() {
+    String result = stub.analyzeSentiment("This product is average");
+    assertEquals("Neutral", result);
+  }
+}