UsbPlayerTest.quieter_10_Test third Case

src/main/java/device/usbPlayer/UsbPlayer.java

@@ -113,6 +113,9 @@ public class UsbPlayer implements Device {
 
     public void quieter_10(){
         Lautstaerke -= 10;
+        if (Lautstaerke < 0) {
+            Lautstaerke = 0;
+        }
     }
 
     @Override

src/test/java/device/usbPlayer/UsbPlayerTest.java

@@ -180,10 +180,13 @@ void louderTest(String testName, UsbPlayer inputPlay, int expectedResult) {
             up2.quieter_10();
         }
 
+        UsbPlayer up3 = new UsbPlayer();
+        up3.quieter_10();
 
         return Stream.of(
                 Arguments.of("Volume was 10, should be 0 ", up1, 0),
-                Arguments.of("Volume was 50, should be 20 ", up2, 20)
+                Arguments.of("Volume was 50, should be 20 ", up2, 20),
+                Arguments.of("Volume was 0, should stay 0 ", up3, 0)
         );
     }