Truncate the test data in Magento

This script will start you over, remember to backup first!

SET FOREIGN_KEY_CHECKS=0;

TRUNCATE `sales_order`;
TRUNCATE `sales_order_datetime`;
TRUNCATE `sales_order_decimal`;
TRUNCATE `sales_order_entity`;
TRUNCATE `sales_order_entity_datetime`;
TRUNCATE `sales_order_entity_decimal`;
TRUNCATE `sales_order_entity_int`;
TRUNCATE `sales_order_entity_text`;
TRUNCATE `sales_order_entity_varchar`;
TRUNCATE `sales_order_int`;
TRUNCATE `sales_order_text`;
TRUNCATE `sales_order_varchar`;
TRUNCATE `sales_flat_quote`;
TRUNCATE `sales_flat_quote_address`;
TRUNCATE `sales_flat_quote_address_item`;
TRUNCATE `sales_flat_quote_item`;
TRUNCATE `sales_flat_quote_item_option`;
TRUNCATE `sales_flat_order_item`;
TRUNCATE `sendfriend_log`;
TRUNCATE `tag`;
TRUNCATE `tag_relation`;
TRUNCATE `tag_summary`;
TRUNCATE `wishlist`;
TRUNCATE `log_quote`;
TRUNCATE `report_event`;

ALTER TABLE `sales_order` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_datetime` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_decimal` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity_datetime` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity_decimal` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity_int` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity_text` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_entity_varchar` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_int` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_text` AUTO_INCREMENT=1;
ALTER TABLE `sales_order_varchar` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_quote` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_quote_address` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_quote_address_item` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_quote_item` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_quote_item_option` AUTO_INCREMENT=1;
ALTER TABLE `sales_flat_order_item` AUTO_INCREMENT=1;
ALTER TABLE `sendfriend_log` AUTO_INCREMENT=1;
ALTER TABLE `tag` AUTO_INCREMENT=1;
ALTER TABLE `tag_relation` AUTO_INCREMENT=1;
ALTER TABLE `tag_summary` AUTO_INCREMENT=1;
ALTER TABLE `wishlist` AUTO_INCREMENT=1;
ALTER TABLE `log_quote` AUTO_INCREMENT=1;
ALTER TABLE `report_event` AUTO_INCREMENT=1;

-- reset customers
TRUNCATE `customer_address_entity`;
TRUNCATE `customer_address_entity_datetime`;
TRUNCATE `customer_address_entity_decimal`;
TRUNCATE `customer_address_entity_int`;
TRUNCATE `customer_address_entity_text`;
TRUNCATE `customer_address_entity_varchar`;
TRUNCATE `customer_entity`;
TRUNCATE `customer_entity_datetime`;
TRUNCATE `customer_entity_decimal`;
TRUNCATE `customer_entity_int`;
TRUNCATE `customer_entity_text`;
TRUNCATE `customer_entity_varchar`;
TRUNCATE `log_customer`;
TRUNCATE `log_visitor`;
TRUNCATE `log_visitor_info`;

ALTER TABLE `customer_address_entity` AUTO_INCREMENT=1;
ALTER TABLE `customer_address_entity_datetime` AUTO_INCREMENT=1;
ALTER TABLE `customer_address_entity_decimal` AUTO_INCREMENT=1;
ALTER TABLE `customer_address_entity_int` AUTO_INCREMENT=1;
ALTER TABLE `customer_address_entity_text` AUTO_INCREMENT=1;
ALTER TABLE `customer_address_entity_varchar` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity_datetime` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity_decimal` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity_int` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity_text` AUTO_INCREMENT=1;
ALTER TABLE `customer_entity_varchar` AUTO_INCREMENT=1;
ALTER TABLE `log_customer` AUTO_INCREMENT=1;
ALTER TABLE `log_visitor` AUTO_INCREMENT=1;
ALTER TABLE `log_visitor_info` AUTO_INCREMENT=1;

-- Reset all ID counters
TRUNCATE `eav_entity_store`;
ALTER TABLE `eav_entity_store` AUTO_INCREMENT=1;

SET FOREIGN_KEY_CHECKS=1;

Magento Customer Password Encryption

Magento follows the below steps to encrypt the password. This encypted passowrd will be stored in the database.

Let suppose your password will be "test123". Magento will add auto generated slot variable for this password. Let the auto-generated slot is "BJ".

The following is code for generating the hash.
echo Mage::helper('core')->getHash('test123', 'BJ');

Printed variable is the one stroed in the database.