code: public function isUpToDate(): bool
      {
          if (! $this->isTracking()) {
              throw new GitException(
                  'Error: HEAD does not have a remote tracking branch. Cannot check if it is up-to-date.'
              );
          }
  
          $mergeBase = $this->run('merge-base', ['@', '@{u}']);
          $remoteSha = $this->run('rev-parse', ['@{u}']);
          return $mergeBase === $remoteSha;
      }
docs: Returns whether HEAD is up-to-date with its remote tracking branch.