try

$installer->addAttribute('customer', 'testveri', array(
    'label' => 'Working?',
    'input' => 'select',
    'type'  => 'int',
    'forms' => array('adminhtml_customer'),
    'source'  => 'eav/entity_attribute_source_boolean',
    'required' => 0,
    'user_defined' => 0,
));

try

$installer->addAttribute('customer', 'testveri', array(
    'label' => 'Working?',
    'input' => 'select',
    'type'  => 'int',
    'source'  => 'eav/entity_attribute_source_boolean',
    'required' => 0,
    'user_defined' => 0,
));

$attributeCode='testveri';
$attribute = Mage::getSingleton('eav/config')
    ->getAttribute('customer', $attributeCode);
$attribute->setData('used_in_forms', array('adminhtml_customer'));
$attribute->save();