class TokenFixture extends BaseFixture{
  async build(taskName){
    this.srcDir// acess to src dir
    await this.readSrcFile(filename);
    // User do their work.
    await this.writeActualFile(filename, content);
  }
}
describe('test',function(){
  const fixture = new TokenFixture(__dirname);
  fixture.runTask(async item=>{
    it(item.name,item=>fixture.build(item));
  });
})
// 在每个runtask之后要处理一下actualfile和expectfile比较的问题，根据比较结果决定当前用例是否通过。