Add test illustrating how to use AsRef<[u8]> for MaxBuffer

This test shows how to hide the type being returned from a function
that moves out MaxBuffer. This way clients can hide the implementation
detail (MaxBuffer).

Signed-off-by: Wiktor Kwapisiewicz <[email protected]>

Author: wiktor-k

tss-esapi/tests/integration_tests/structures_tests/buffers_tests/max_buffer_tests.rs

@@ -47,4 +47,17 @@ mod test_auth {
             assert_eq!(expected, actual);
         }
     }
+
+    #[test]
+    fn test_as_ref() {
+        // The following function accepts the broadest selection of types as its argument
+        // including MaxBuffer. It also returns the MaxBuffer but in such a way that the
+        // client is not aware of the true underlying type.
+        fn accepts_returns_as_ref(data: impl AsRef<[u8]>) -> tss_esapi::Result<impl AsRef<[u8]>> {
+            let data = data.as_ref();
+            let max_buffer = MaxBuffer::from_bytes(data)?;
+            Ok(max_buffer)
+        }
+        accepts_returns_as_ref(MaxBuffer::from_bytes(&[1, 2, 3]).unwrap()).unwrap();
+    }
 }