Add verify-exercises-in-docker script

[keiravillekode]

This useful script from generic-track tests exercise(s) against the test runner.

Like bin/test-exercise,
we splice the exercise's example solution with the unittest block from the source.

[github-actions]

Hello 👋 Thanks for your PR.

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[IsaacG]

Prefer return to exit where viable

[IsaacG]

Suggested change

	count=0
	for exercise_dir in ./exercises/{concept,practice}/${exercise_slug}/; do
	if [[ -d "${exercise_dir}" ]]; then
	verify_exercise "${exercise_dir}"
	((++count))
	fi
	done
	((count > 0)) || die 'no matching exercises found!'
	exercises=(./exercises/{concept,practice}/${exercise_slug}/)
	(( "${#exercises[@]}" == 0 )) && die 'no matching exercises found!'
	for exercise_dir in "${exercises[@]}"; do
	verify_exercise "${exercise_dir}"
	done

[keiravillekode]

I have kept the count variable.

We want to report 'no matching exercises found!' when the user mistypes an exercise slug.

[IsaacG]

FWIW I used this file as a base to build a Go verify-in-docker script: https://github.com/IsaacG/fork-exercism-go/blob/main/bin/verify-exercises-in-docker
Feel free to copy anything you like in there :)