Database Connectivity Error

[Die Hard]

Query to select database:
$select = mysql_select_db($db_table, $con);
I have connected database by require() function.
<?php
require(connection.php)
$select=mysql_select_db($test);
if ($select)
{
echo "database selected";
}
else {
echo "database not selected";
}
?>

This showed the error and output was: database not selected.
Where is error?