fix: propagate config.group to test group when attached_node is null

[waterWang]

Fix: config.group propagation for unattached test nodes

When a data test has no attached_node (source tests and singular tests), dbt-core 1.x copies the explicit config.group into the test's group property, but the Fusion engine leaves it null. This causes --select group:xxx and state:modified to give different results between the two engines.

Root cause

In resolve_data_tests.rs, the group field on DbtTestAttr was set only from the parent model's group:

let group = attached_node
    .as_deref()
    .and_then(|id| models.get(id))
    .and_then(|m| m.__model_attr__.group.clone());

When attached_node is None (source tests, singular tests), this always produced None, even when the test had an explicit config.group.

Fix

When attached_node is None, fall back to test_config.group (the explicit config value). Generic tests on models/seeds/snapshots continue to inherit the parent node's group.

Fixes: #15930

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[larspettermadsstuen]

@waterWang will you complete required steps for this, or is this abandoned? Keen to get this fixed, happy to open a new pr.

[Thrasi]

@larspettermadsstuen I am very eager as well but @waterWang might be very preoccupied with all the work they have been doing in August:

@HannanNaeem How can this move forward?

[larspettermadsstuen]

@larspettermadsstuen I am very eager as well but @waterWang might be very preoccupied with all the work they have been doing in August

Busy bee indeed. Not too hopeful of an update, so I made a "competing" PR here.

[aiguofer]

Thanks for your contribution! I'm closing this PR and moving forward with #16265