Add tests for default impls of Frontend req handlers

Add tests to assert return values (and existence) of default implemenation
of VhostUserFrontendReqHandler and VhostUserFrontendReqHandlerMut trait
methods.

Signed-off-by: Matej Hrica <mhrica@redhat.com>

Author: mtjhrc

vhost/src/vhost_user/frontend_req_handler.rs

@@ -396,6 +396,7 @@ mod tests {
     use super::*;
 
     use std::collections::HashSet;
+    use std::io::ErrorKind;
 
     use uuid::Uuid;
 
@@ -455,6 +456,72 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_default_frontend_impl() {
+        struct Frontend;
+        impl VhostUserFrontendReqHandler for Frontend {}
+
+        let f = Frontend;
+        assert_eq!(
+            f.shared_object_add(&Default::default()).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shared_object_remove(&Default::default())
+                .unwrap_err()
+                .kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shared_object_lookup(&Default::default(), &0)
+                .unwrap_err()
+                .kind(),
+            ErrorKind::Unsupported
+        );
+
+        assert_eq!(
+            f.shmem_map(&Default::default(), &0).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shmem_unmap(&Default::default()).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+    }
+
+    #[test]
+    fn test_default_frontend_impl_mut() {
+        struct FrontendMut;
+        impl VhostUserFrontendReqHandlerMut for FrontendMut {}
+
+        let mut f = FrontendMut;
+        assert_eq!(
+            f.shared_object_add(&Default::default()).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shared_object_remove(&Default::default())
+                .unwrap_err()
+                .kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shared_object_lookup(&Default::default(), &0)
+                .unwrap_err()
+                .kind(),
+            ErrorKind::Unsupported
+        );
+
+        assert_eq!(
+            f.shmem_map(&Default::default(), &0).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+        assert_eq!(
+            f.shmem_unmap(&Default::default()).unwrap_err().kind(),
+            ErrorKind::Unsupported
+        );
+    }
+
     #[test]
     fn test_new_frontend_req_handler() {
         let backend = Arc::new(Mutex::new(MockFrontendReqHandler::new()));