test: round-trip the no_std IntentBody derive probe

crates/no-std-probe/src/lib.rs

@@ -1,5 +1,10 @@
-//! Compile-only `#![no_std]` probe: `#[derive(IntentBody)]` must expand
-//! without the consumer's std prelude or an `extern crate alloc`.
+//! `no_std` derive-hygiene probe for `#[derive(IntentBody)]`. The claim
+//! is scoped to the derive, not the whole SDK: the expansion names only
+//! `::core` and the SDK's `__private` re-exports (borsh, `alloc`), so it
+//! compiles without the consumer's std prelude or an `extern crate
+//! alloc`. The crate is `#![no_std]`; the `tests` module (std-exempt)
+//! exercises an actual encode/decode round-trip, so the generated codec
+//! is verified correct, not merely expanded.
 
 #![no_std]
 #![warn(missing_docs)]
@@ -12,3 +17,31 @@ pub enum ProbeBody {
     /// First published version.
     V1(u8),
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use videre_sdk::BodyError;
+
+    #[test]
+    fn round_trip() {
+        let body = ProbeBody::V1(7);
+        let bytes = body.to_bytes().expect("encode");
+        // One-byte version tag (0) then the borsh u8 payload.
+        assert_eq!(bytes, [0u8, 7u8]);
+        assert_eq!(ProbeBody::from_bytes(&bytes).expect("decode"), body);
+    }
+
+    #[test]
+    fn unknown_version() {
+        assert!(matches!(
+            ProbeBody::from_bytes(&[9, 7]),
+            Err(BodyError::UnknownVersion { version: 9 }),
+        ));
+    }
+
+    #[test]
+    fn empty() {
+        assert!(matches!(ProbeBody::from_bytes(&[]), Err(BodyError::Empty)));
+    }
+}