function svgTest_newOneFieldBlock() {
  Blockly.Blocks['one_field_block'] = {
    init: function() {
      this.jsonInit({
        'message0': '%1',
        'args0': [
          {
            'type': 'field_input',
            'name': 'FIELD'
          }
        ]
      });
    }
  };

  var block = svgTest_workspace.newBlock('one_field_block');
  block.initSvg();
  block.render(false);
  return block;
}
Create a block with one field. Must be called after svgTest_setUp().
@return {!Blockly.Block} The new block with one field.