shutterstock-package: Shutterstock API client
In shutterstock: Access 'Shutterstock' REST API

The endpoint descriptions are retrieved from Shutterstock API Reference documentation.

Insert unit tests by using testthat package
Copy .httr-oauth file into tests/testthat directory (but remove that later)
Add/uncomment httptest::start_capturing() and httptest::stop_capturing() recording lines between the tests
Run specific tests one by one e.g. devtools::test(filter = "audio")
When the API files are created/updated, remove/comment the recording lines
Wrap tests with with_mock_api calls
Run the tests again with the same filter
Done if all tests pass. Move to the next one.

To make the package dev structure loose coupled, the name of the parameters passed to a call are not hard-coded in the code. The parameters are handled by the HTTP requests which receive the parameters from function calls by the ellipsis (...).
For the calls containing that kind of parameters are validated by e.g. check_required_args(id, "numeric"). It is considered as required especially if that parameter is tied to a URL.