Hi Sai,

I updated the code and commented on the line where error was comming. Plz follow that comment.

@istest
private class TestClass {
    @testSetup static void setup() {
        Id profileId = [SELECT Id FROM Profile WHERE Name='Standard User'].Id; //Update here filter criteria according to your req.
        List<String> ContinentList = new List<String>{'Asia', 'Africa', 'Antarctica', 'Europe', 'Australia'};
        List<String> RegionList = new List<String>{'East', 'West', 'North', 'South', 'North-East'};
        List<String> MarketList = new List<String>{'Market-1', 'Market-2', 'Market-3', 'Market-4', 'Market-5'};
        
        List<User> userList = new List<User>();
        List<Region__c> lstRegion = new List<Region__c>();
        List<Market__c> lstMarket = new List<Market__c>();
        
        for(Integer index = 0; index < 5; index++){
            Region__c objReg = new Region__c(
                                            Name = RegionList[index]
                                            ); 
            
            
            lstRegion.add(objReg);
            
        }
        insert lstRegion;
		
		for(Integer index = 0; index < 5; index++){
			Market__c objMar = new Market__c(
                                            Name = MarketList[index],
                                            Region__c = lstRegion[index].Id  
                                            ); //Market having look up with region
			lstMarket.add(objMar);
		}
        for(Integer index = 0; index < 5; index++) {
            userList.add(createTestUser(profileId, 'Test-' + index, 'User', ContinentList[index], MarketList[index], RegionList[index]));
        }
        
        //insert all test data.
        try{
            insert userList;
            insert lstMarket;
        }
        catch(Exception ex) {
            system.debug('---Exception---' + ex);
        }
    }
   
    @istest static void  testClassMethod() {
        
        Test.startTest();
            List<User> lstUsers = [Select Id, Name From User];
            
            system.runAs(lstUsers[0]){
                QuickCreateController quickCreateCont = new QuickCreateController();  // error in this line : Note > Check  whether this class "QuickCreateController" is a Abstract class or not, If it is then create instance of any extended class and pass as param to below line. 
				//Like:  <Your Extended Class Name> absInst = new <Your Extended Class Name>();
                OpportunityQuickCreateExt objClass = new OpportunityQuickCreateExt(quickCreateCont); // Then pass here "absInst" as parameter.
            }
        Test.stopTest();
    }
    
    private static User createTestUser(Id profID, String fName, String lName, String Continent, String Market, String Region) {
        String orgId = userInfo.getOrganizationId();
        String dateString = String.valueof(Datetime.now()).replace(' ','').replace(':','').replace('-','');
        Integer randomInt = Integer.valueOf(math.rint(math.random()*1000000));
        String uniqueName = orgId + dateString + randomInt;
        User tuser = new User(  firstname = fName,
                                lastName = lName,
                                email = uniqueName + '@test' + orgId + '.org',
                                Username = uniqueName + '@test' + orgId + '.org',
                                EmailEncodingKey = 'ISO-8859-1',
                                Alias = uniqueName.substring(18, 23),
                                TimeZoneSidKey = 'America/Los_Angeles',
                                LocaleSidKey = 'en_US',
                                LanguageLocaleKey = 'en_US',
                                ProfileId = profId,
                                Default_Continent__c = '',
                                Default_Market__c = '',
                                Default_Region__c = ''
                                );
        return tuser;
    }
}

Note: Check whether this class "QuickCreateController" is a Abstract class or not, If it is then create instance of any extended class and pass as param to below line. Like:
<Your Extended Class Name> absInst = new <Your Extended Class Name>();
OpportunityQuickCreateExt objClass = new OpportunityQuickCreateExt(absInst); // Then pass here "absInst" as parameter.


Hope it will help you.