Fix serialised size assumptions from #48.

Unfortunately the serialised size is likely never going to be the same
as the type's size in memory, as most serialisation formats define
additional headers for parsing safety reasons, such as buffer lengths
and type information.

src/ed25519.rs

@@ -1645,9 +1645,6 @@ mod test {
     #[cfg(all(test, feature = "serde"))]
     use bincode::{serialize, serialized_size, deserialize, Infinite};
 
-    #[cfg(all(test, feature = "serde"))]
-    use std::mem::size_of;
-
     #[cfg(all(test, feature = "serde"))]
     #[test]
     fn serialize_deserialize_signature() {
@@ -1681,25 +1678,19 @@ mod test {
     #[cfg(all(test, feature = "serde"))]
     #[test]
     fn serialize_public_key_size() {
-        assert_eq!(
-            serialized_size(&PUBLIC_KEY) as usize,
-            size_of::<PublicKey>()
-        );
+        assert_eq!(serialized_size(&PUBLIC_KEY) as usize, 40); // These sizes are specific to bincode==1.0.1
     }
 
     #[cfg(all(test, feature = "serde"))]
     #[test]
     fn serialize_signature_size() {
         let signature: Signature = Signature::from_bytes(&SIGNATURE_BYTES).unwrap();
-        assert_eq!(serialized_size(&signature) as usize, size_of::<Signature>());
+        assert_eq!(serialized_size(&signature) as usize, 72); // These sizes are specific to bincode==1.0.1
     }
 
     #[cfg(all(test, feature = "serde"))]
     #[test]
     fn serialize_secret_key_size() {
-        assert_eq!(
-            serialized_size(&SECRET_KEY) as usize,
-            size_of::<SecretKey>()
-        );
+        assert_eq!(serialized_size(&SECRET_KEY) as usize, 40); // These sizes are specific to bincode==1.0.1
     }
 }