Positive coverage: is_not_downstream / via normalize

1 test exercised this rule:

Source location: tests/coherence_orphan.rs:196

#[test]
fn CoreTraitLocal_for_AliasToKnown_in_Foo() {
    // TODO: see comment in `orphan_check` from prev commit
    FormalityTest::new(crates![crate core {
        trait CoreTrait<T> {}

        trait Unit {
            type Assoc : [];
        }

        impl<T> Unit for T {
            type Assoc = ();
        }
    },
    crate foo {
        struct FooStruct {}
        impl CoreTrait<FooStruct> for <() as Unit>::Assoc {}
    }])
    .skip_execute()
    .ok()
}