added new test case for next() & changed next() to work with regional and saved stations

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

@@ -114,9 +114,15 @@ public class RadioPlayer implements Device {
 
     @Override
     public void next() {
-        int currentIndex = savedPlaylist.indexOf(playedStation);
-        int nextIndex = (currentIndex + 1) % savedPlaylist.size();
-        playedStation = savedPlaylist.get(nextIndex);
+        if (regionPlaylist.contains(playedStation)){
+            int currentIndex = regionPlaylist.indexOf(playedStation);
+            int nextIndex = (currentIndex + 1) % regionPlaylist.size();
+            playedStation = regionPlaylist.get(nextIndex);
+        } else {
+            int currentIndex = savedPlaylist.indexOf(playedStation);
+            int nextIndex = (currentIndex + 1) % savedPlaylist.size();
+            playedStation = savedPlaylist.get(nextIndex);
+        }
     }
 
     @Override

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

@@ -75,14 +75,18 @@ class RadioPlayerTest {
         RadioPlayer rp1 = new RadioPlayer();
         RadioPlayer rp2 = new RadioPlayer();
         RadioPlayer rp3 = new RadioPlayer();
+        RadioPlayer rp4 = new RadioPlayer();
         rp1.next();
         rp2.next();
         rp2.prev();
         rp3.prev();
+        rp4.changeRegion("BY");
+        rp4.next();
         return Stream.of(
-                Arguments.of("Next Station Test", rp1, "Teddy"),
-                Arguments.of("Prev Station Test", rp2, "YouFM"),
-                Arguments.of("Prev works on first Station ", rp3, "MegaHits")
+                Arguments.of("Next Station Test for saved Stations", rp1, "Teddy"),
+                Arguments.of("Prev Station Test for saved Stations", rp2, "YouFM"),
+                Arguments.of("Prev works on first Station for saved Stations", rp3, "MegaHits"),
+                Arguments.of("changed Region and going to next station", rp4, "Bayern 1")
         );
     }