added third test case for changeOrderInSavedPlaylist() & and added productive code

src/main/java/device/radioPlayer/RadioPlayer.java

@@ -216,11 +216,16 @@ public class RadioPlayer implements Device {
         if((nr-1) > savedPlaylist.size()) {
             savedPlaylist.remove(playedStation);
             savedPlaylist.add(savedPlaylist.size(),station);
-            return"Station " + playedStation + " is now on place 0" + nr + "in saved playlist";
-        } else {
+            return"Station " + playedStation + " is now on place 0" + (savedPlaylist.size()+1) + "in saved playlist";
+        }else if(nr < 0) {
+            savedPlaylist.remove(playedStation);
+            savedPlaylist.add(0,station);
+            return"Station " + playedStation + " is now on place 01 in saved playlist";
+        }
+        else {
             savedPlaylist.remove(playedStation);
             savedPlaylist.add(nr - 1, station);
-            return "Station " + playedStation + " is now on place 0" + (savedPlaylist.size()+1) + "in saved playlist";
+            return "Station " + playedStation + " is now on place 0" + nr + "in saved playlist";
         }
     }
 }

src/test/java/device/radioPlayer/RadioPlayerTest.java

@@ -279,10 +279,14 @@ class RadioPlayerTest {
         rp.changeOrderInSavedPlaylist(1);
         RadioPlayer rp1 = new RadioPlayer();
         rp1.changeOrderInSavedPlaylist(5);
+        RadioPlayer rp2 = new RadioPlayer();
+        rp2.next();
+        rp2.changeOrderInSavedPlaylist(-1);
 
         return Stream.of(
                 Arguments.of("Test for change order in saved playlist with nr isn`t bigger than playlist size", rp, 0, "Teddy"),
-                Arguments.of("Test for change order in saved playlist with nr is than bigger playlist size but at the end of playlist", rp1, 2, "YouFM")
+                Arguments.of("Test for change order in saved playlist with nr is than bigger playlist size put at the end of playlist", rp1, 2, "YouFM"),
+                Arguments.of("Test for change order in saved playlist with nr is than smaller than 0 at front of playlist", rp2, 0, "Teddy")
         );
     }
 }