Menu callback; generate warnings to test the error handler.
function error_test_generate_warnings($collect_errors = FALSE) {
// Tell Drupal error reporter to send errors to Simpletest or not.
define('SIMPLETEST_COLLECT_ERRORS', $collect_errors);
// This will generate a notice.
$monkey_love = $bananas;
// This will generate a warning.
$awesomely_big = 1 / 0;
// This will generate a user error.
trigger_error("Drupal is awesome", E_USER_WARNING);
return "";
}