Ryuichi Okumura, a developer, is using Sauce Labs' WebDriver protocol with Yeti to test JavaScript applications. He has set up a testing environment using Sauce Labs and Yeti to run tests on multiple browsers and devices in the cloud. The process involves signing up for a Sauce Labs account, installing the necessary tools, and running the tests using the `yeti` command-line interface. With this setup, developers can test their applications in various browser and device combinations without needing physical hardware. Ryuichi's use of Sauce Labs and Yeti showcases the potential of cloud-based testing services for automating JavaScript testing environments.