`_can_pass_early` with `missing`

[theogf]

It's me again!

I have an issue on one of my test_rrule involving missing values. The _can_pass_early test fails to pass as both actual and expected are equal to missing. Naturally missing == missing returns missing and make the test fails. Using isequal solves the issue but I guess that's also not the wanted behaviour.

Any clue on how to solve this?

[oxinabox]

When we thought about this before, we were like "Let's not spend to much time thinking about this, when is a tangent actually going to be missing"
so we didn't think on it too hard.

Can you tell more about why that tangent is missing?
It will help us determine what the correct behavour is.

[theogf]

So the Tangent itself is not missing, it is already properly set to NoTangent and after more care, I would argue it's more a problem of #271 where missing actually comes from to_vec with FiniteDifferences producing ismissing. In the context of test_approx, iszero(missing) is called and hence the missing comparison.

[oxinabox]

I see.
Yeah so it was getting expected wrong because FiniteDifferences couldn't handle it,
and actual was not infact set to missing.

Sounds like we should either change it so that that _can_pass_early should return false (rather than erroring with missing but that's low priority.
I guess it would be an easy check to add as ismissing(expected) but also if you are ended up with expected===missing probably something else is wrong anyway and so the error is kinda more useful?

So maybe we can close this?