Add tests to check when a language is added several times

[ValMati]

• Test that verifies that a language added twice is counted only once
• Test that proves that a language added twice is correctly deleted

pull request

Although it is not made explicit in the exercise, I believe that it should be understood that a language should be added only once.

Looking forward to your feedback. :)

---

Reviewer Resources:

Track Policies

[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!

[kahgoh]

I am going to decline this one. I don't see the point in adding this requirement. This is an exercise on Lists. In Java, if you want a collection where each item can be appear only once, I'd suggest using a Set instead.

[kahgoh]

I am going to decline this one. I don't see the point in adding this requirement. This is an exercise on Lists. In Java, if you want a collection where each item can be appear only once, I'd suggest using a Set instead.