Sync tests

[jiegillet]

Closes #1605

A few new tests for 3 exercises. They all passed, so I didn't split the PR.

[github-actions]

Thank you for contributing to exercism/elixir 💜 🎉. This is an automated PR comment 🤖 for the maintainers of this repository that helps with the PR review process. You can safely ignore it and wait for a maintainer to review your changes.

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• Any exercise changed

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• Practice exercise changed

  • 🌲 Do prerequisites, practices, and difficulty in config.json need to be updated?
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• Practice exercise tests changed

  • ⚪️ Are all tests except the first one skipped?
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Automated comment created by PR Commenter 🤖.

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[angelikatyborska]

Thanks!