I tried to get up below class coverage from 62% to 100% but no luck..
what i am missing...?Please help me out...bold code in test class has not covered...

Apex class:

public with sharing class InvoiceGenerator {

    public void generateInvoices() { 
        Invoice_Generation_Frequency__c igf = Invoice_Generation_Frequency__c.getInstance('Default');
        system.debug('igf.Days__c:'+igf.Days__c);
                               
        Integer currentYear = system.today().year();
        Integer currentDay = (system.today().addDays((integer)igf.Days__c)).day();
        system.debug('--day--'+currentDay);
         
        List<Account> accList = [Select Id,Group__c,Group_Signup_Start_Date__c,Group_Renewal_Date__c,Invoice_Amount__c From Account  where
 
  Group__c='yes' and CALENDAR_YEAR(Group_Renewal_Date__c) < = :currentYear and DAY_IN_MONTH(Group_Renewal_Date__c) = :currentDay];
         
        String currYear = system.today().year() + '%';
        //List<AggregateResult> arList = [select count(id) cnt from Invoice__c where Invoice_Number__c like :currYear];
        //nextInvNum = (integer)arList[0].get('cnt');
       
        List<Invoice__c> invnumberList = [select Invoice_Number__c from Invoice__c where Invoice_Number__c like:currYear order by Invoice_Number__c desc];
        List<Invoice__c> InvoiceList = new List<Invoice__c>();
       
  if(invnumberList.size() > 0){ 
            string invhighestnum = invnumberList[0].Invoice_Number__c;
         string convertedlast = invhighestnum.substring(5,9);
         integer InvNumhighest = integer.valueOf(convertedlast);
         system.debug('132654'+InvNumhighest); 
        
         system.debug('--InvNumhighestnew--'+InvNumhighest); 
         for(Account a : accList) {
          InvNumhighest++;
             Invoice__c Inv = new Invoice__c();
             Inv.Account__c = a.Id; 
             Inv.Paid__c = false;
             Inv.Group_Start_Date__c = a.Group_Signup_Start_Date__c;
             Inv.Group_Renewal_Date__c = a.Group_Renewal_Date__c;
             Inv.Invoice_Amount__c = a.Invoice_Amount__c; 
             Inv.Invoice_Number__c = (system.today().year() + '-' + InvNumhighest);
             InvoiceList.add(Inv);
             system.debug('--invList--'+InvoiceList);
   }
   insert InvoiceList;
  }
  else {
          integer nextInvNum;
          nextInvNum = 0000;                  
          nextInvNum = nextInvNum + 2000;
    system.debug('--nextInvNum--'+nextInvNum);
     for(Account a : accList) {
      nextInvNum++;
              Invoice__c Inv = new Invoice__c();
              Inv.Account__c = a.Id; 
              Inv.Paid__c = false;
              Inv.Start_Date__c = a.Group_Signup_Start_Date__c;
              Inv.Renewal_Date__c = a.Group_Renewal_Date__c;
              Inv.Invoice_Amount__c = a.Invoice_Amount__c;
              Inv.Invoice_Number__c = (system.today().year() + '-' + nextInvNum);
              InvoiceList.add(Inv); 
     }
     insert InvoiceList;
   }                       
    }
}

Test class:

@isTest(SeeAllData=true)
class TestInvoiceUpdate{
 

public static String CRON_EXP = '0 00 01 * * ?';

static testmethod void test() {
 
   Test.startTest();
  
   Account a = new Account();
    a.Name = 'test';
    a.Group__c = 'Yes';
    Date myDate = date.newinstance((system.today().addYears(-1)).year(), (system.today().addDays(45)).month(), (system.today().addDays(45)).day());
    a.Group_Renewal_Date__c = myDate;
    insert a;
    system.debug('Myinsert'+a);
   
    Invoice__c i = new Invoice__c();
    i.Paid__c = false;
    i.Account__c = a.id;
    i.Invoice_Number__c = '1111';
    insert i;
    
   String InvId = System.schedule('testBasicScheduledApex',CRON_EXP,new InvoiceUpdate());
   // Get the information from the CronTrigger API object
   CronTrigger ct = [SELECT Id, CronExpression, TimesTriggered, NextFireTime FROM CronTrigger WHERE id = :InvId];
   // Verify the expressions are the same
   System.assertEquals(CRON_EXP, ct.CronExpression);
   // Verify the job has not run
   System.assertEquals(0, ct.TimesTriggered);
   Test.stopTest();
  
    }
   
    static testmethod void test1() {
 
    Test.startTest();
  
   Account a = new Account();
    a.Name = 'test1';
    a.Group__c = 'Yes';
    Date myDate1 = date.newinstance((system.today().addYears(-1)).year(), (system.today().addDays(45)).month(), (system.today().addDays(45)).day());
    a.Group_Renewal_Date__c = myDate1;
    insert a;
    system.debug('Myinsert'+a);
   
    Invoice__c i = new Invoice__c();
    i.Paid__c = false;
    i.Account__c = a.id;
    i.Invoice_Number__c = '2222';
    insert i;
    
   String InvId = System.schedule('testBasicScheduledApex',CRON_EXP,new InvoiceUpdate());
   // Get the information from the CronTrigger API object
   CronTrigger ct = [SELECT Id, CronExpression, TimesTriggered, NextFireTime FROM CronTrigger WHERE id = :InvId];
   // Verify the expressions are the same
   System.assertEquals(CRON_EXP, ct.CronExpression);
   // Verify the job has not run
   System.assertEquals(0, ct.TimesTriggered);
   Test.stopTest();
    }    
}