test: add codegen fidelity tests for generated structs

atrium-api/tests/codegen_fidelity.rs

@@ -0,0 +1,39 @@
+//! Fidelity tests for the code generated by `atrium-codegen`.
+//!
+//! These assert properties of the *generated code itself* — the shape of the
+//! `Collection` impl and its agreement with `KnownRecord` — so they are not
+//! coupled to the contents of any particular lexicon revision.
+
+#![cfg(feature = "namespace-appbsky")]
+
+use atrium_api::app::bsky::actor::ContentVisibilityDeclaration;
+use atrium_api::record::KnownRecord;
+use atrium_api::types::Collection;
+
+/// `app.bsky.actor.contentVisibilityDeclaration` is the first record whose NSID
+/// leaf is camelCase, and it broke an assumption in codegen: the NSID was
+/// rebuilt from the snake_case'd file stem, so the record never matched its own
+/// schema and got no `Collection` impl. `KnownRecord` is keyed on schema ids, so
+/// it *did* gain the variant — leaving downstream crates with an arm they could
+/// not satisfy.
+#[test]
+fn camel_case_record_nsid_is_generated_verbatim() {
+    const NSID: &str = "app.bsky.actor.contentVisibilityDeclaration";
+
+    // Naming `NSID` at all requires the `Collection` impl to exist; the
+    // assertions require it to carry the NSID verbatim, rather than a
+    // snake_case'd or otherwise mangled form.
+    assert_eq!(ContentVisibilityDeclaration::NSID, NSID);
+    assert_eq!(ContentVisibilityDeclaration::nsid().as_str(), NSID);
+}
+
+/// The `Collection` and `KnownRecord` halves must *agree* on the record type,
+/// not merely both exist. This is never called: it is a compile-time assertion,
+/// and fails to build if the `Collection` impl disappears again or its `Record`
+/// drifts from the type the corresponding `KnownRecord` variant holds.
+#[allow(dead_code)]
+fn collection_record_is_the_known_record_payload(
+    record: <ContentVisibilityDeclaration as Collection>::Record,
+) -> KnownRecord {
+    KnownRecord::AppBskyActorContentVisibilityDeclaration(Box::new(record))
+}