Magento – Source model not found error message when exporting customer info

Your XML looks correct — although if Magento's loading the class from the Mage namespace that may be because your XML hasn't been loaded into the global configuration tree (cached XML, incorrect app/etc/modules file).

Your best bet is to debug things at the point where Magento looks into the configuration for your new class name

#File: app/code/core/Mage/Core/Model/Config.php
public function getGroupedClassName($groupType, $classId, $groupRootNode=null)
{
    //..
    $config = $this->_xml->global->{$groupType.'s'}->{$group};
    $className = null;
    if (isset($config->rewrite->$class)) {
        $className = (string)$config->rewrite->$class;
    } else {
    //..
}

Figure out why Magento can't find your base classname in the XML configuration, and you'll have your problem solved.

Dropdown cannot get it Source model

macerier_test/system_config_source_dropdown_values that why it showing the error

May be you did not define model prefix.

As per as your code macerier_test . is models prefix

So let define model prefix at config.xml

config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Macerier_TEST>
            <version>0.1.0</version>
        </Macerier_TEST>
    </modules>
    <!-- add this -->
    <global>
    <models>
        <macerier_test> <!-- call as model prefix identifier -->
            <class>Macerier_TEST_Model</class>
        </macerier_test>
    </models>
    </global>

</config>