Standardize: should we use t() for assertion messages or not?

All throughout core there are simpletests with gazillions of assertions and some of them use t() on the second parameter and some dont. Which is correct? Once we decide which is correct I think we should go through and fix...

Example (from form.test):
$this->assertNoFieldByXPath('//th[@class="select-all"]', NULL, t('Do not display a "Select all" checkbox when #multiple is FALSE, even when #js_select is TRUE.'));

Example (from shortcut.test):
$this->assertFalse(in_array($set->links[0]['mlid'], $mlids), 'Successfully deleted a shortcut.');