Hi Sonam ,

Thanks for the help...
So for EX if I am having a class 
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public class TVRemoteControl {
    // Volume to be modified
    Integer volume;
    // Constant for maximum volume value
    static final Integer MAX_VOLUME = 50;   
   
    // Constructor
    public TVRemoteControl(Integer v) {
        // Set initial value for volume
        volume = v;
    }
       
    public Integer increaseVolume(Integer amount) {
        volume += amount;
        if (volume > MAX_VOLUME) {
            volume = MAX_VOLUME;
        }
        return volume;
    }
   
    public Integer decreaseVolume(Integer amount) {
        volume -= amount;
        if (volume < 0) {
            volume = 0;
        } 
        return volume;
    }   
   
    public static String getMenuOptions() {
        return 'AUDIO SETTINGS - VIDEO SETTINGS';
    }
      
}
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When I will write the test case - 

@isTest
class TVRemoteControlTest {
    @isTest static void testVolumeIncrease() {
        TVRemoteControl rc = new TVRemoteControl(10);
        Integer newVolume = rc.increaseVolume(15);
        System.assertEquals(25, newVolume);
    }
   
    @isTest static void testVolumeDecrease() {
        TVRemoteControl rc = new TVRemoteControl(20);
        Integer newVolume = rc.decreaseVolume(15);
        System.assertEquals(5, newVolume);       
    }
       
    @isTest static void testVolumeIncreaseOverMax() {
        TVRemoteControl rc = new TVRemoteControl(10);
        Integer newVolume = rc.increaseVolume(100);
        System.assertEquals(50, newVolume);       
    }
   
    @isTest static void testVolumeDecreaseUnderMin() {
        TVRemoteControl rc = new TVRemoteControl(10);
        Integer newVolume = rc.decreaseVolume(100);
        System.assertEquals(0, newVolume);       
    }
   
    @isTest static void testGetMenuOptions() {
        // Static method call. No need to create a class instance.
        String menu = TVRemoteControl.getMenuOptions();
        System.assertNotEquals(null, menu);
        System.assertNotEquals('', menu);
    }
}
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Can TVRemoteControl rc = new TVRemoteControl be initialised once and can be reused.

Regards