Function is_test_function 

pub fn is_test_function(tcx: TyCtxt<'_>, fn_def_id: LocalDefId) -> bool

Checks if fn_def_id has a #[test] attribute applied

This only checks directly applied attributes. To see if a node has a parent function marked with #[test] use is_in_test_function.

Note: Add //@compile-flags: --test to UI tests with a #[test] function