Fixed most reported issues by SonarCloud.

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

@@ -23,15 +23,23 @@
 
 package com.iluwatar.composite;
 
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 /**
  * Application test
  */
-public class AppTest {
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   *
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link App#main(String[])}
+   * throws an exception.
+   */
 
   @Test
-  public void test() {
-    App.main(new String[]{});
+  void shouldExecuteApplicationWithoutException() {
+    Assertions.assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }