Storing as a Static Test Fixture

If a useful_thing is costly to create, in terms of time or memory. It can be saved in the tests/testthat/fixtures/ folder, but with its corresponding companion R script.

.
├── ...
└── tests
    ├── testthat
    │   ├── fixtures
    │   │   ├── make-useful-things.R
    │   │   ├── useful_thing1.rds
    │   │   └── useful_thing2.rds
    │   ├── helper.R
    │   ├── setup.R
    │   └── (all the test files)
    └── testthat.R