dependencies: #2449 bump maven-checkstyle-plugin from 3.1.0 to 3.2.0 + resolve chec… (#2464)

* #2449 bump maven-checkstyle-plugin from 3.1.0 to 3.2.0 + resolve checkstyle issues

* remove FileSelectorJFrame.java to resolve checkstyle issue

* remove FileSelectorJFrame.java to resolve checkstyle issue

* remove FileSelectorJFrame.java to resolve checkstyle issue

* add refactored file with correct filename to resolve checkstyle issue

* add the test data

* change filenames from JFrame to Jframe for checkstyle

* fix code smell from  sonar report

* add new testcases to improve the test coverage

* remove code smell

extension-objects/src/test/java/concreteextensions/CommanderTest.java

@@ -31,7 +31,6 @@ import ch.qos.logback.core.read.ListAppender;
 import org.junit.jupiter.api.Test;
 import org.slf4j.LoggerFactory;
 import units.CommanderUnit;
-
 import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;

extension-objects/src/test/java/concreteextensions/SergeantTest.java

@@ -31,7 +31,6 @@ import ch.qos.logback.core.read.ListAppender;
 import org.junit.jupiter.api.Test;
 import org.slf4j.LoggerFactory;
 import units.SergeantUnit;
-
 import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;