code: public function renderProgressMark(MutantResult $result, $count, $current, $eolInterval = 60)
      {
          $this->progressCount++;
  
          switch ($result->getResult()) {
              case MutantResult::TIMEOUT:
                  $this->write('<fg=cyan;options=bold>T</fg=cyan;options=bold>', false);
                  break;
              case MutantResult::ERROR:
                  $this->write('<fg=yellow;options=bold>E</fg=yellow;options=bold>', false);
                  break;
              case MutantResult::ESCAPE:
                  $this->write('<fg=red;options=bold>M</fg=red;options=bold>', false);
                  break;
              case MutantResult::KILL:
              default:
                  $this->write('<options=bold>.</options=bold>', false);
                  break;
          }
  
          if (($this->progressCount % $eolInterval) == 0) {
              $counter = str_pad($this->progressCount, 5, ' ', STR_PAD_LEFT);
              $this->write(
                  ' |' . $counter . ' ('
                  . str_pad($current, strlen($count), ' ', STR_PAD_LEFT)
                  . '/' . $count . ')' . PHP_EOL,
                  false
              );
          }
      }
docs: Render a progress marker:
  T: The test run timed out, possibly due to an infinite loop or underestimated timeout
  E: The test run hit a fatal error, either kicked out from a test or due to a Humbug issue
  M: The test run was successful. The mutation went undetected by the unit tests.
  .: The test run included a fail condition. The mutation was detected!!!
  
  @param MutantResult $result
  @param int $count
  @param int $current
  @param int $eolInterval