Sync strain tests

[BNAndras]

Related to #1597. Mark as tiny.

The test suite uses slightly different functions so I updated those to match what's happening in the problem specifications. There shouldn't be any meaningful differences there. I also changed the words to be an array literal so it's a little clearer what's actually being compared before and after. That included a minor typo fix. Finally, I added two missing tests for keeps nothing and discards nothing

[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!

[BNAndras]

Hmm, I thought defining the predicates outside the function call like we did over in Accumulate would fix the @typescript-eslint/no-unused-vars error.