test method to cover for loop

To cover the for loop, you need to create the Account data setup in test class and call your dummy method.This will work for your test coverage.

@isTest
private class CreateDummyAccountTest
{
    @testsetup
       static void createAccount()
       {
            List<Account> accList= new List<Account>();        
            for(Integer i = 0 ; i<5 ; i++) 
            {
                 accList.add(new Account(Name= 'testAccountName'+i ));
            } 
            insert accList;
        }
	static testMethod void test()
	{
		 List<Account> accountList=[SELECT Id,Name FROM Account];
		 CreateDummyAccount.dummyMethod(accountList);
		 system.assert(!accountList.isEmpty());
	}    
}