Why smarty template engine won't find my template file?

Question

Why smarty template engine won't find my template file?

Fatal error: Uncaught --> Smarty: Unable to load template file 'test.tpl' <-- thrown in C:\xampp\htdocs\testing\includes\smarty\sysplugins\smarty_internal_templatebase.php on line 129

also did $smarty->testInstall();

Smarty Installation test...
Testing template directory...
C:\xampp\htdocs\testing\templates\frontend\default\tpl is OK.
Testing compile directory...
C:\xampp\htdocs\testing\templates_c\frontend is OK.
Testing plugins directory...
C:\xampp\htdocs\testing\includes\smarty\plugins is OK.
Testing cache directory...
C:\xampp\htdocs\testing\cache is OK.
Testing configs directory...
C:\xampp\htdocs\testing\configs is OK.
Testing sysplugin files...
... OK
Testing plugin files...
... OK
Tests complete.

And var_dump($smarty->getTemplateDir());

array(1) { [0]=> string(55) "C:/xampp/htdocs/testing/templates/frontend/default/tpl\" }

File schema

htdocs
    -- testing
        -- incluses
            -- smarty
                plugins
                sysplugins
                Smarty.class.php
                SmartyBC.class.php
            -- configs
                configs.php
            -- db
                connect.php
                db.php
        -- configs
        -- cache
        -- templates
            -- frontend
                -- default
                    -- css
                    -- mages
                    -- js
                    -- tpl
                        test.tpl
            -- backend
        -- templates_c
            -- frontend
        index.php

index.php

<?php

ini_set('display_errors', 1);
ini_set('log_errors', 1);
ini_set('display_startup_errors', TRUE);
ini_set('error_log', dirname(__FILE__) . '/error_log.txt');
error_reporting(E_ALL);

ob_start();
session_start();

require 'includes/smarty/Smarty.class.php';
require 'includes/db/db.php';
require 'includes/configs/configs.php';

$page = isset($_GET['do']) ? $_GET['do'] : '';

switch($page){

    case 'home';
    include 'pages/home.php';
    break;

    default:
    include 'pages/test.php';
    break;

}

ob_flush();

?>

configs.php

<?php

$smarty = new Smarty();
$smarty->compile_check = true;
$smarty->debugging = false;
$smarty->cache = 1;
$smarty->setTemplateDir('C:/xampp/htdocs/testing/templates/frontend/default/tpl');
$smarty->setCompileDir('C:/xampp/htdocs/testing/templates_c/frontend/default');
$smarty->setCacheDir('C:/xampp/htdocs/testing/cache');
$smarty->setConfigDir('C:/xampp/htdocs/testing/configs'); 

?>

test.php

<?php

//$success = 'Success Message';
//$error = 'Error Message';
$errors[] = 'Error one';
$errors[] = 'Error two';

$smarty = new Smarty;
//$smarty->assign('success', $success);
//$smarty->assign('error', $error);
$smarty->assign('errors', $errors);
$smarty->display('test.tpl');

?>

test.tpl

{if !empty($errors)}
<div id="errors">
{section name=i loop=$errors}
{$errors[i]}<br />
{/section}
</div>
{/if}

Answer 1

Confusing as it was to debug this, it is really down to a simple matter of the global variable $smarty, which was a Smarty object initially set in configs.php, being overwritten again when test.php was included. Smarty lost its configured $template_dir because the object $smarty was reinitialized to defaults. The default location for templates is to look in ./templates, which is why it worked to use C:/xampp/htdocs/testing/templates/test.tpl.

Solution: just don't do $smarty = new Smarty(); inside test.php

test.php

<?php

//$success = 'Success Message';
//$error = 'Error Message';
$errors[] = 'Error one';
$errors[] = 'Error two';

// Don't do this:  $smarty is already initialized and configured.
// $smarty = new Smarty;

$smarty->assign('errors', $errors);
$smarty->display('test.tpl');

?>