Over onHeine apparently found and patched an unrelated bug in the SearchExcerpt test D7 version:
$longtext = str_repeat($text . ' ', 10); - $result = preg_replace('| +|', ' ', search_excerpt('nothing', $text)); + $result = preg_replace('| +|', ' ', search_excerpt('nothing', $longtext)); $this->assertTrue(strpos($result, $expected) === 0, 'When keyword is not found in long string, return value starts as expected');
This fix needs to get into Drupal 8 and then be backported to D7. I'm moving it to a new issue. Can someone make a quick patch please?