Method mute of CDPlayer tested on checkingTheReturnValue -> ShouldReturnAString.

src/main/java/device/cdPlayer/CDPlayer.java

@@ -109,7 +109,7 @@ public class CDPlayer implements Device {
 
     @Override
     public String mute() {
-        return null;
+        return ("Volume muted.");
     }
 
     @Override

src/test/java/device/cdPlayer/CDPlayerTest.java

@@ -493,7 +493,7 @@ class CDPlayerTest {
 
     @ParameterizedTest
     @MethodSource("addToFavoriteSongsData")
-    void addToFavoriteSongs(String testName,String cases, CDPlayer _cdPlayer,Exception exception) {
+    void addToFavoriteSongsTest(String testName,String cases, CDPlayer _cdPlayer,Exception exception) {
         if(cases.equals("Case1")) {
             String myFavoriteSong = _cdPlayer.getCD().getPlayList()[0];
             _cdPlayer.addToFavoriteSongs(myFavoriteSong);
@@ -531,4 +531,19 @@ class CDPlayerTest {
         );
     }
 
+    @ParameterizedTest
+    @MethodSource("muteTestData")
+    void muteTest(String testName,String cases, CDPlayer _cdPlayer,String expectedResult) {
+        assertThat(_cdPlayer.mute()).describedAs(testName).isEqualTo(expectedResult);
+    }
+    static Stream<Arguments> muteTestData () {
+        CDPlayer cdPlayer1 = new CDPlayer();
+        return Stream.of(
+                Arguments.of("[mute() by checkingTheReturnValue ] => ShouldReturnAString", "Case1", cdPlayer1, "Volume muted.")
+        );
+    }
+
+
+
+
     }