Change label_replace and label_join test cases to fail when either legacy or UTF-8 name validation is enabled

[charleskorn]

The existing PromQL test cases test that label_replace and label_join return an error when the destination label name is invalid.

However, these test cases fail when UTF-8 name validation is enabled, and this is now the default as of prometheus/common#724.

In this PR, I've changed the invalid destination label name to something that is invalid with both the legacy and UTF-8 validation schemes. I've taken this value from the corresponding test cases in Prometheus itself.

[ywwg]

because we still support both UTF-8 and legacy validation (and will do so forever, from my understanding), I create two types of tests:

• failures under legacy but not UTF-8
• failures under both legacy and UTF-8

So I would suggest making these tests in addition, rather than replacing, the existing legacy-failing tests

[charleskorn]

because we still support both UTF-8 and legacy validation (and will do so forever, from my understanding), I create two types of tests:

• failures under legacy but not UTF-8
• failures under both legacy and UTF-8

So I would suggest making these tests in addition, rather than replacing, the existing legacy-failing tests

Thanks for the feedback. Do we need to exercise both groups in this test suite? My understanding is that this test suite isn't intended to exhaustively test every feature, but cover the important cases.

If you do want to cover both groups: is there an existing pattern for enabling / disabling particular test cases based on feature flags enabled on the target instance? I don't see one, but didn't want to make up something if I've missed something somewhere.