/**
 * We are expecting a mail to have been created, and to contain a pattern
 */
public function findInMail($grep, $mail_index = -1) {
  $mails = $this->drupalGetMails();
  if ($mail_index == -1) {
    $last_mail = end($mails);
  }
  elseif ($mail_index < 0) {
    $index = count($mails) + $mail_index;
    $this->assertTrue($index >= 0, 'We are looking for an email with a valid index (' . $index . ')');
    if (!isset($mails[$index])) {
      $this->assertTrue(FALSE, 'There are ' . count($mails) . ' in total but we are trying to look in mail # ' . $index);
    }
    $last_mail = $mails[$index];
  }
  else {
    $last_mail = $mails[$mail_index];
  }
  if (!$last_mail) {
    $this->assertTrue(FALSE, 'There are no mails to look in');
    return;
  }
  if (!isset($last_mail['body'])) {
    $this->assertTrue(FALSE, 'A mail has been sent by the system but does not contain a body element');
    $this->inspect($last_mail);
    return;
  }
  $body = $last_mail['body'];
  if (!drupal_strlen($body)) {
    $this->assertTrue(FALSE, 'A mail has been sent by the system, it contains a body element, but not text');
    $this->inspect($last_mail);
    return;
  }
  $matches = array();
  $result = $this->pregMatch($grep, $body, $matches, TRUE);
  if (isset($matches[1])) {
    $this->assertTrue(isset($matches[1]), 'We found ' . $grep . ': ' . $matches[1] . ': ' . $result);
    return $matches[1];
  }
  $this->assertTrue(isset($matches[0]), 'We found ' . $grep . ': ' . $matches[0] . ': ' . $result);
  return $matches[0];
}

public function pregMatch($grep, $body, &$matches = array(), $expecting = FALSE) {
  // see http://stackoverflow.com/questions/3710454
  $old_error = error_reporting(0); // Turn off error reporting

  $result = preg_match($grep, $body, $matches);
  if ($result === 0 && $expecting) {
    $this->inspect($body);
    $this->assertTrue(FALSE, 'We were expecting to find the pattern ' . htmlentities($grep) . ' but it is not there. Inspecting the haystack (which has a length of ' . drupal_strlen($body) . ') in the preceding line.');
  }
  else {
    $this->assertTrue(TRUE, 'As expected, we found the  pattern ' . $grep . '.. Inspecting the haystack (which has a length of ' . drupal_strlen($body) . ') in the following line.');
    $this->inspect($body);
  }
  if ($result === FALSE) {
    $this->assertTrue(FALSE, 'An error occurred searching for the pattern ' . $grep . ': ' . $error["message"] . '. Inspecting the body in the following line');
    $this->inspect($body);
  }
  error_reporting($old_error);  // Set error reporting to old level

  return $result;
}

/**
 * Inspect a structured data on the test page.
 *
 * Useful for debugging.
 */
public function inspect($x) {
  try {
    $this->verbose('<pre>' . print_r($x, TRUE) . '</pre>');
  }
  catch(Exception $e) {
    $this->assertTrue(FALSE, 'Error ' . $e->getMessage() . '  while trying to display : ' . serialize($x));
  }
}