In Routine§
See primary documentation in context for trait is test-assertion
multi trait_mod:<is>(Routine:D, :$test-assertion!)
Declares that a routine generates test output (aka TAP). When failures are reported, the calling routine's location is used instead of this routine. For example:
use Test; sub foo-test($value) is test-assertion { is $value, 42, "is the value 42?"; } foo-test(666); # <-- error is reported on this line