Batch Class:

global class BatchAccount implements Database.Batchable<sObject> 
{
    global Database.QueryLocator start(Database.BatchableContext BC) {
		
        return Database.getQueryLocator('SELECT Id,Name FROM Account');
    }
	
    global void execute(Database.BatchableContext BC, List<Account> scope) {
		
        for(Account a : scope)
        {
            a.Name = a.Name + ' Updated';
        }
        update scope;
    }
	
    global void finish(Database.BatchableContext BC) {
		
    }
}

Test Class:

@isTest 
public class BatchAccountTest 
{
    static testMethod void test() 
    {
        List<Account> accList = new List<Account>();
        for(Integer i = 0 ; i < 200; i++)
        {
            Account acc = new Account();
            acc.Name = 'Name' + i;
            accList.add(acc);
        }
        Insert accList;
        
		Test.startTest();
		BatchAccount obj = new BatchAccount();
		DataBase.executeBatch(obj); 
		Test.stopTest();
		
		//Verify accounts updated
		List<Account> accUpdatedList = [SELECT Id, Name FROM Account];
		System.assert(accUpdatedList[0].Name.Contains('Updated'));
    }
}