Rust: add more thourough canonical path testing

rust/schema/annotations.py

@@ -844,12 +844,10 @@ class _:
 
 
 @annotate(AssocItemList)
+@qltest.test_with(Trait)
 class _:
     """
-    A AssocItemList. For example:
-    ```rust
-    todo!()
-    ```
+    A list of  `AssocItem` elements, as appearing for example in a `Trait`.
     """
 
 
@@ -1541,11 +1539,18 @@ class _:
 
 
 @annotate(Trait)
+@rust.doc_test_signature(None)
 class _:
     """
     A Trait. For example:
-    ```rust
-    todo!()
+    ```
+    trait Frobinizable {
+      type Frobinator;
+      type Result: Copy;
+      fn frobinize_with(&mut self, frobinator: &Self::Frobinator) -> Result;
+    }
+
+    pub trait Foo<T: Frobinizable> where T::Frobinator: Eq {}
     ```
     """