function createBlockMock() {
      return {
        id: 'test',
        rendered: false,
        workspace: {
          rendered: false,
        },
        renameVarById: Blockly.Block.prototype.renameVarById,
        updateVarName: Blockly.Block.prototype.updateVarName,
        isShadow: () => false,
        isDeadOrDying: () => false,
      };
    }
Create a mock block that may be used as the source block for a field.
@returns {!Object} Mock block.