diff --git a/src/main/java/device/Device.java b/src/main/java/device/Device.java
index a2a8c3f..276e029 100644
--- a/src/main/java/device/Device.java
+++ b/src/main/java/device/Device.java
@@ -7,6 +7,7 @@ public interface Device {
 	int getVolume();
 	void next();
 	void prev();
+	String play();
 	//get deviceName, Album and current Item
 	String getInfoText();
 	//get a list of public methods
@@ -15,6 +16,8 @@ public interface Device {
 	String chooseItem(int itemNr);
 	// get the actual album
 	String[] getItemList();
-	String play();
-
+	//mute the Volume and returns an Info.
+	String mute();
+	//unmute the Volume and returns an Info.
+	String unmute();
 	}
diff --git a/src/main/java/device/cdPlayer/CDPlayer.java b/src/main/java/device/cdPlayer/CDPlayer.java
index bdf1995..f5f93cc 100644
--- a/src/main/java/device/cdPlayer/CDPlayer.java
+++ b/src/main/java/device/cdPlayer/CDPlayer.java
@@ -90,6 +90,16 @@ public class CDPlayer implements Device {
         return loadedCD.getPlayList();
     }
 
+    @Override
+    public String mute() {
+        return null;
+    }
+
+    @Override
+    public String unmute() {
+        return null;
+    }
+
     @Override
     public String play() {
         if(isCdFlapOpen()){
diff --git a/src/main/java/device/radioPlayer/RadioPlayer.java b/src/main/java/device/radioPlayer/RadioPlayer.java
index 849fb11..d7f35f1 100644
--- a/src/main/java/device/radioPlayer/RadioPlayer.java
+++ b/src/main/java/device/radioPlayer/RadioPlayer.java
@@ -188,6 +188,16 @@ public class RadioPlayer implements Device {
         return null;
     }
 
+    @Override
+    public String mute() {
+        return null;
+    }
+
+    @Override
+    public String unmute() {
+        return null;
+    }
+
 
     @Override
     public String play() {
diff --git a/src/main/java/device/usbPlayer/UsbPlayer.java b/src/main/java/device/usbPlayer/UsbPlayer.java
index bf403d6..b1440e3 100644
--- a/src/main/java/device/usbPlayer/UsbPlayer.java
+++ b/src/main/java/device/usbPlayer/UsbPlayer.java
@@ -160,6 +160,16 @@ public class UsbPlayer implements Device {
         return null;
     }
 
+    @Override
+    public String mute() {
+        return null;
+    }
+
+    @Override
+    public String unmute() {
+        return null;
+    }
+
 
     @Override
     public String play() {
diff --git a/src/test/java/device/cdPlayer/CDPlayerTest.java b/src/test/java/device/cdPlayer/CDPlayerTest.java
index dd985ed..3bcc1db 100644
--- a/src/test/java/device/cdPlayer/CDPlayerTest.java
+++ b/src/test/java/device/cdPlayer/CDPlayerTest.java
@@ -1,12 +1,18 @@
 package device.cdPlayer;
 
+import device.Device;
 import device.cdPlayer.exceptions.*;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.mockito.junit.jupiter.MockitoExtension;
 
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.stream.Stream;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -231,22 +237,39 @@ class CDPlayerTest {
 
     @ParameterizedTest
     @MethodSource("getOptionsTestData")
-    void getOptionsTest(String testName,String testDirection, CDPlayer _cdPlayer, String expectedResult){
+    void getOptionsTest(String testName,String testDirection, CDPlayer _cdPlayer){
         if(testDirection.equals("ReturnValueNotNull")) {
             assertThat(_cdPlayer.getOptions()).describedAs(testName).isNotEqualTo(null);
         }
         if(testDirection.equals("ArrayLengthGreaterThen0")) {
             assertThat(_cdPlayer.getOptions().length).describedAs(testName).isNotEqualTo(0);
         }
+        if(testDirection.equals("ArrayContainsInterfaceMethods")) {
+            Method[]interfaceMethods=Device.class.getDeclaredMethods();
+            List<String> deviceMethods = new ArrayList<String>(Arrays.asList(_cdPlayer.getOptions()));
+            for (int i = 0; i < interfaceMethods.length; i++) {
+                assertThat(deviceMethods.contains(interfaceMethods[i].getName())).describedAs(testName).isEqualTo(true);
+            }
+        }
     }
     static Stream<Arguments> getOptionsTestData () {
         CDPlayer cdPlayer1 = new CDPlayer();
         return Stream.of(
-                Arguments.of("[getOptions(): shouldNotReturnNull] => ReturnValueNotNull", "ReturnValueNotNull", cdPlayer1,null),
-                Arguments.of("[getOptions(): shouldReturnAnArrayWithLengthGreaterThen0] => ArrayLengthGreaterThen0", "ArrayLengthGreaterThen0", cdPlayer1,null)
+                Arguments.of("[getOptions(): shouldNotReturnNull] => ReturnValueNotNull", "ReturnValueNotNull", cdPlayer1),
+                Arguments.of("[getOptions(): shouldReturnAnArrayWithLengthGreaterThen0] => ArrayLengthGreaterThen0", "ArrayLengthGreaterThen0", cdPlayer1),
+                Arguments.of("[getOptions(): shouldReturnAnArrayWithInAllInterfaceMethods] => ArrayContainsInterfaceMethods", "ArrayContainsInterfaceMethods", cdPlayer1)
         );
     }
 
-
+    @Test
+    void getVolumeReturnValueBetween0And100(){
+        CDPlayer cdPlayer1 = new CDPlayer();
+        boolean volumeIstInValueRange=false;
+        int volume=cdPlayer1.getVolume();
+        if(volume>=0 && volume <=100){
+            volumeIstInValueRange=true;
+        }
+        assertThat(volumeIstInValueRange).isEqualTo(true);
+    }
 
 }
\ No newline at end of file