leap: Fix loophole in unit tests

[cruxicheiros]

Currently, it's possible to pass all the unit tests by checking if (year % 4 == 0) && (year % 100 == year % 400).

This commit changes one of the test cases so that this is no longer possible. Note that this is a separate issue to #955 -- however, 1996, like 2020, is not divisible by 16, so that loophole will remain closed.

EDIT
This post formerly stated, incorrectly, that it was possible to pass the unit tests by checking (year % 100) == (year % 400).

[stkent]

Nice catch, thanks for the PR!

[rpottsoh]

Nice job! Thanks.

[petertseng]

it's possible to pass all the unit tests by checking if (year % 100) == (year % 400)

I was unable to verify that this statement is true.

The first case is 2015.

2015 % 100 == 2015 % 400 is 15 == 15 is true, whereas the expected answer is false. So a solution that checks whether (year % 100) == (year % 400) will fail, as it should.

Did you mean to cite a different improperly-passing solution?

[cruxicheiros]

@petertseng PR #979 in exercism/python. Sorry for any confusion.

What I meant to say was that it was possible to pass the unit test by checking (year % 4 == 0) && (year % 100 == year % 400)

[petertseng]

So, the solution in question also checks year % 4 == 0 so as to be able to correctly reject 2015, which was not stated in the PR.

This means that the commit message was incorrect. We all need to be more careful that commit messages are correct.

I considered rewriting master to amend the commit message, but I suppose it's too discourteous to ask everyone who already acquired that commit to reset it away.

I considered recommending that the commit be reverted, then reapplied with a correct message, but perhaps as long as GitHub continues to exist, this written record is sufficient, but now needs an internet connection to be able to see it.

[cruxicheiros]

I've edited the body of the pull request so that it contains the correct information for anyone who checks on GitHub.

In future PRs I will triple-check that what I am writing is correct. Again, I apologise.

[Insti]

In future PRs I will triple-check that what I am writing is correct. Again, I apologise.

❤️

We all miss things sometimes. @stkent, @cmccandless and @rpottsoh also missed this.

It's the responsibility of the reviewers to help catch these issues so they can be fixed before the pull request is merged. That's why we have reviews.