feat: Clean Architecture (#3235)

* #3230 - Clean Architecture.

* #3230 - Clean Architecture.

* #3230 - Clean Architecture.

* #3230 - Clean Architecture.

* #3230 - Clean Architecture Sonar.

* #3230 - Clean Architecture Sonar.

* #3230 - Clean Architecture Sonar.

* #3230 - Clean Architecture Sonar.

---------

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

clean-architecture/src/test/java/com/iluwatar/cleanarchitecture/AppTest.java

@@ -0,0 +1,20 @@
+package com.iluwatar.cleanarchitecture;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+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}
+   * throws an exception.
+   */
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}