Add YAML REST tests for percentile_ranks metric aggregation

[polyfractal]

More YAML REST tests for aggregations. Pretty straightforward :)

Related to #26220

[polyfractal]

retest this please

[cbuescher]

@elasticmachine test this please

[colings86]

@polyfractal is this still something you want to get merged? I'm a bit dubious about having YAML tests that check the exact values coming from algorithms like t-digest since it means that any update to improve the algorithm breaks the test, IMO we should have unit tests that check that the algorithm is working as expected and use the YAML tests to just check the API does what it's supposed to.

/cc @elastic/es-search-aggs

[polyfractal]

Yes, I agree... these exact-value tests are super flaky and easy to break.

I'll see if I can pare these tests down to something that uses the agg's DSL without checking the actual values. Although I suspect there won't be a lot to actually test since the parameters directly affect the values and nothing else.

[colings86]

I wonder if instead of check for an exact value we could instead check it is within an expected error of the accurate value given the data set is small? e.g. we could check in these tests that it is within 2% of the actual value

[polyfractal]

Yep, that'd work. I thought about it at the time, but the yaml tests don't have an easy way to do it... you have to do use two checks (gte + lte) for each value, and I was feeling lazy :P

Perhaps just spot check a few values with the gte/lte pairs?

[colings86]

Perhaps just spot check a few values with the gte/lte pairs?

👍

[polyfractal]

Closing for now, almost certainly needs updating and don't have time at the moment.