Implement two tests for the rust playground:
- successful run of the hello world example with the hello world message
in stdout and a hidden stderr
- on purpose compilation error is shown in stderr and "No output" in
stdout
This is a first draft for a test framework for testing the JS part of
the book that is discussed in #2462
It is using [webdriverIO](https://webdriver.io/) and the webdriverIO
[Expect API](https://webdriver.io/docs/api/expect-webdriverio/) in
combination with [Mocha](https://mochajs.org/). WebdriverIO is taking
care of accessing the webpage with a real browser and can access the
state of the page so behavior can be asserted.
Currently only a small test for the speaker-notes implementation demos
the functionality.
The [Static Server
Service](https://webdriver.io/docs/static-server-service/) is used to
serve the book in a way that the test runner can access it.
A CI integration can look like https://webdriver.io/docs/githubactions/
and is implemented with a headless setup. In CI it uses the language
variable to set environment variable that configures where the built
book should be mounted from
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Co-authored-by: Martin Geisler <martin@geisler.net>
