Fixed datepicker positioning calculation

[oojacoboo]

See #2057. This still needs merging.

[linux-foundation-easycla]

• ✅login: oojacoboo / (6a2872c)

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[mgol]

Thanks for the PR. We'll need tests for this change, though, as I indicated in the other PR. Have a look at existing test in https://github.com/jquery/jquery-ui/tree/main/tests/unit/datepicker to see how to write one.

[oojacoboo]

@mgol these are unit tests. Can you please explain what about this change needs to be added or updated with unit tests? As for integration tests, which is actually the only way to add tests around this - does this lib even have those? And if so, can you please direct me to one as an example where you can test the visibility of the datepicker's location within a browser window?

[mgol]

We only have unit tests. While I agree some tests would better work as integration ones, most of the changes can be tested via unit tests.

I'd start with constructing a runnable example on a platform like JS Bin where the issue is obvious - this would be useful for people looking at the reasons for this patch in the future as well. Then we can think about a possible test case that would represent what we saw.

If you don't have any idea for how the unit test would look like, start with a runnable example and maybe I'll be able to propose something.

[oojacoboo]

@mgol How are you going to write a unit test for something that's dynamically calculated based on a browser window's scroll position?

[mgol]

Tests are run on real browsers, the HTML files used for tests are also defined by us. You can scroll programmatically as long as you make sure there’s enough content to have something to scroll even on large screens.