Method mute of CDPlayer tested on 6x louder()-> mute() -> getOldVolumeShouldReturn_0.

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

@@ -122,6 +122,7 @@ public class CDPlayer implements Device {
     public String unmute() {
         muted=false;
         volume=oldVolume;
+        oldVolume=0;
         return ("Volume unmute.");
     }
 

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

@@ -584,13 +584,23 @@ class CDPlayerTest {
             assertThat(_cdPlayer.isMuted()).describedAs(testName).isEqualTo(false);
             assertThat(_cdPlayer.getVolume()).describedAs(testName).isEqualTo(5);
         }
+        if(cases.equals("Case4")) {
+            for (int i = 0; i < 6; i++) {
+                _cdPlayer.louder();
+            }
+            _cdPlayer.mute();
+            _cdPlayer.unmute();
+            assertThat(_cdPlayer.isMuted()).describedAs(testName).isEqualTo(false);
+            assertThat(_cdPlayer.getOldVolume()).describedAs(testName).isEqualTo(0);
+        }
     }
     static Stream<Arguments> unmuteTestData () {
         CDPlayer cdPlayer1 = new CDPlayer();
         return Stream.of(
                 Arguments.of("[unmute() by checkingTheReturnValue ] => ShouldReturnAString", "Case1", cdPlayer1, "Volume unmute."),
                 Arguments.of("[unmute() by checkingTheEffectAfterRun ] => VariableMutedShouldBeFalse", "Case2", cdPlayer1, "Volume unmute."),
-                Arguments.of("[unmute() by 5x louder()-> mute()] => getVolumeShouldReturn_5", "Case3", cdPlayer1, "Volume unmute.")
+                Arguments.of("[unmute() by 5x louder()-> mute()] => getVolumeShouldReturn_5", "Case3", cdPlayer1, "Volume unmute."),
+                Arguments.of("[unmute() by 6x louder()-> mute()] => getOldVolumeShouldReturn_0", "Case4", cdPlayer1, "Volume unmute.")
         );
     }