Hi,
Below Code is the VF page and Controller for MultiSelect Picklist and also the test Class, But the code Coverage is 89%.
Can anyone please help me for 100% code coverage.
<apex:page controller="MultiSelectController">
    <style>
        .box{
            width :100px;
            length : 100px;
        
        }
    </style>
    <apex:form >
        <apex:panelGrid id="one" columns="3">
            <apex:selectList multiselect="true" styleClass="checkbox" value="{!added}">
                <apex:selectOptions value="{!selected}"></apex:selectOptions>
            </apex:selectList>
            <apex:panelGrid columns="1">
                <apex:commandButton action="{!addcities}" value="ADD" reRender="one"/>
                <apex:commandButton action="{!delcities}" value="DEL" reRender="one"/>
            </apex:panelGrid>
            <apex:selectList multiselect="true" styleClass="check" value="{!deleted}">
                <apex:selectOptions value="{!unSelected}"></apex:selectOptions>
            </apex:selectList>
        </apex:panelGrid>
            
    </apex:form>
</apex:page>
-----------------------------------------------------
public class MultiSelectController {
    public List<String> added{get;set;}
    public List<String> deleted{get;set;}
    public List<SelectOption> selected{get;set;}
    public List<SelectOption> unSelected{get;set;}
    public Set<String> sel{get;set;}
    public set<String> unsel{get;set;}
    
    public MultiSelectController(){
    added = new List<string>();
    deleted = new List<String>();
        sel = new Set<string>();
    unsel= new Set<String>();
    selected = new List<SelectOption>();
    unSelected = new List<selectOption>();
        List<String> cities = new List<String>{'HYD','Bang','Delhi','Pune','Mumbai'};
            unsel.addAll(cities);
        getData();
    }
    public void getData(){
        selected.clear();
        unSelected.clear();
        SelectOption op1 = new SelectOption('none','-None-');
        if(unsel.size()>0){
            for(String s1 : unsel){
                SelectOption op = new SelectOption(s1,s1);
               selected.add(op);
            }
           
        }
         else{
              Selected.add(op1);  
            }
            
        if(sel.size()>0){
            for(String s2:sel){
            selectOption op2 = new Selectoption(s2,s2);
                unSelected.add(op2);
                }
        }
        else{
            unselected.add(op1);
        }
    }
    public void addcities(){
    unsel.removeAll(added);
      sel.addAll(added);
      added.clear();
        getData();  
    }
    public void delcities(){
      sel.removeAll(deleted);
     unsel.addAll(deleted);
        getData();     
    }
}
----------------------------------------
@isTest
public class MiltiSelectTest {
      public static testMethod void TestController(){
      PageReference pagref = Page.MiltiSelect;
        Test.setCurrentPageReference(pagref);
          test.startTest();
          MultiSelectController MSP = new MultiSelectController();
          //MSP.addcities()
          MSP.addcities();
          MSP.delcities();
          MSP.getData();
          //MSP.unsel;
      test.stopTest();
      }

}