$this->assertEqual(form_type_checkbox_value($form,$edit),$default_value,t('form_type_checkbox_value() returns the default value when #disabled is set.'));
// Element is not disabled, $edit is not empty.
unset($form['#disabled']);
$this->assertEqual(form_type_checkbox_value($form,$edit),$return_value,t('form_type_checkbox_value() returns the return value when #disabled is not set.'));
// Element is not disabled, $edit is empty.
$edit=array();
$this->assertIdentical(form_type_checkbox_value($form,$edit),0,t('form_type_checkbox_value() returns 0 when #disabled is not set, and $edit is empty.'));
// $edit is FALSE.
$edit=FALSE;
$this->assertNull(form_type_checkbox_value($form,$edit),t('form_type_checkbox_value() returns NULL when $edit is FALSE'));