Louder_test() for UsbPlayer.Louder() implemented

src/test/java/device/UsbPlayerTest.java

@@ -3,6 +3,7 @@ package device;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
 
 class UsbPlayerTest {
 
@@ -10,8 +11,10 @@ class UsbPlayerTest {
 
 
     @Test
-    void louder() {
-       up.setLautstaerke(1);
+    void louder_test() {
+       up.setLautstaerke(40);
+       up.louder();
+       assertThat(up.getLautstaerke()).isEqualTo(41);
     }
 /*
     @Test