前面 1 ~ 4 點，學習一些技巧和寫法，但是效能提升没特別提到
但文章的第 5 點 Efficiently load data records 得到几个方向
- Use let, rather than let!
- One is to use before_all instead of before_each in a test file
- Another is to have a global variables file, which loads an instance of each record before all tests start
- Another approach is to user FactoryBot’s build_stubbed method