docs: double dispatch explanation + refactor (#2915)

double-dispatch/src/test/java/com/iluwatar/doubledispatch/AppTest.java

@@ -35,7 +35,6 @@ 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.
    */

double-dispatch/src/test/java/com/iluwatar/doubledispatch/RectangleTest.java

@@ -52,7 +52,7 @@ class RectangleTest {
    * #toString()}
    */
   @Test
-  void testToString() throws Exception {
+  void testToString() {
     final var rectangle = new Rectangle(1, 2, 3, 4);
     assertEquals("[1,2,3,4]", rectangle.toString());
   }