Fixed most reported issues by SonarCloud.

promise/src/main/java/com/iluwatar/promise/Promise.java

@@ -47,6 +47,7 @@ public class Promise<T> extends PromiseSupport<T> {
    * Creates a promise that will be fulfilled in future.
    */
   public Promise() {
+    // Empty constructor
   }
 
   /**

promise/src/test/java/com/iluwatar/promise/AppTest.java

@@ -26,13 +26,15 @@ package com.iluwatar.promise;
 import java.util.concurrent.ExecutionException;
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 /**
  * Application test.
  */
-public class AppTest {
+class AppTest {
 
   @Test
-  public void testApp() throws InterruptedException, ExecutionException {
-    App.main(null);
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(null));
   }
 }

promise/src/test/java/com/iluwatar/promise/PromiseTest.java

@@ -67,7 +67,7 @@ public class PromiseTest {
 
   @Test
   public void promiseIsFulfilledWithAnExceptionIfTaskThrowsAnException()
-      throws InterruptedException, TimeoutException {
+      throws InterruptedException {
     testWaitingForeverForPromiseToBeFulfilled();
     testWaitingSomeTimeForPromiseToBeFulfilled();
   }