go/doc/next/6-stdlib/99-minor/testing/43936.md

The new methods [T.Attr], [B.Attr], and [F.Attr] emit an attribute to the test log. An attribute is an arbitrary key and value associated with a test.

For example, in a test named TestAttr, t.Attr("key", "value") emits:

=== ATTR  TestAttr key value