anchor.diff:    const testButton  = $('#test-button');
     const testSpinner = $('#test-spinner');
     const testOverlay = $('<div id="test-overlay"></div>');
  +
  +  const form = testButton.closest('form');
   
     testButton.enable = () => {
       testButton.attr('disabled', false);
  
positive.code:           output.val(status + ': is the cyber-dojo server down?');
          }
        },
        complete: (xhr, status) => {
          testSpinner.hide();
          testOverlay.remove();
          testButton.enable();
  
negative.code:     // 3. when you revert
  
      cd.saveCodeFromSyntaxHighlightEditors();
      cd.storeOutgoingFileHashes();
  
      $.ajax({
        timeout: 30000, // 30 seconds (twice server timeout)
           type: 'POST',
            url: form.attr('action'),
           data: form.serialize(),
  
        beforeSend: (_xhr, _settings) => {
          testButton.disable();
          testOverlay.insertAfter($('body'));
          testSpinner.show();
        },
        success: (_data, _status, _xhr) => {
          cd.rebuildFilenameList();
          cd.storeIncomingFileHashes();
        },
        error: (_xhr, status, _thrown) => {
          const output = cd.fileContentFor('output');
          if (status == 'timeout') {
            output.val(status + ': have you lost your network connection?');
  