Adds a new function for deleting files recursively

src/test/java/net/knarcraft/minecraftserverlauncher/utility/JarDownloaderTest.java

@@ -109,12 +109,6 @@ public class JarDownloaderTest {
         if (!target.exists() && !target.mkdirs()) {
             throw new IllegalArgumentException("Unable to create the test files directory");
         }
-        File[] oldFiles = target.listFiles();
-        if (oldFiles == null) {
-            throw new IllegalArgumentException("Unable to list files in jar test directory");
-        }
-        for (File file : oldFiles) {
-            assertTrue(file.delete());
-        }
+        CommonFunctions.removeFilesRecursively(target);
     }
 }