simple-cipher: Add test to disallow mixed case key

[tekerson]

Hi,

During mentoring, I came across a solution that checks if the key is valid (i.e. only contains alpha ascii lower-case letters) by testing

if (key === key.toUpperCase()) {
    throw new Error('Bad key')
}

This passes the current "throws an error with an all caps key" test but allows mixed-case keys, which I believe should actually be invalid. So, I'm proposing a new test to test for this situation.

[tekerson]

It looks like the example implementation fails this test 😮 (I actually didn't even know there was an example implementation… oops).

Is my assumption that the key should only contain lower case characters incorrect, or should I add a fix to the example implementation too?

[masters3d]

Yes please.

[tekerson]

I've updated the example implementation.
The regex was updated to pass the new test.
I did also slightly re-arranged the if..else block to avoid requiring the non-null assertion (!) operator.

But, it looks like CI broke for unrelated reasons;

We had an unexpected error preparing a VM for this build

I'm not sure if I can do anything about that, or if someone just needs to rerun the job?

[masters3d]

Thanks!