test(db): zero-label authority round-trip; doc the labels-json constant

Also fix pre-existing clippy::explicit_auto_deref in all db test files
(&mut *tx → &mut tx across authority.rs and vocab.rs).

crates/db/tests/authority.rs

@@ -24,7 +24,7 @@ async fn authority_round_trips_with_labels(pool: PgPool) {
     let db = Db::from_pool(pool);
 
     let mut tx = db.pool().begin().await.unwrap();
-    let id = authority::create_authority(&mut *tx, &new_person("Carl Larsson", "Carl Larsson"))
+    let id = authority::create_authority(&mut tx, &new_person("Carl Larsson", "Carl Larsson"))
         .await
         .unwrap();
     tx.commit().await.unwrap();
@@ -47,11 +47,11 @@ async fn list_by_kind_filters(pool: PgPool) {
     let db = Db::from_pool(pool);
 
     let mut tx = db.pool().begin().await.unwrap();
-    authority::create_authority(&mut *tx, &new_person("A", "A"))
+    authority::create_authority(&mut tx, &new_person("A", "A"))
         .await
         .unwrap();
     authority::create_authority(
-        &mut *tx,
+        &mut tx,
         &NewAuthority {
             kind: AuthorityKind::Place,
             external_uri: None,
@@ -83,7 +83,7 @@ async fn resolve_authority_returns_kind(pool: PgPool) {
     let db = Db::from_pool(pool);
 
     let mut tx = db.pool().begin().await.unwrap();
-    let id = authority::create_authority(&mut *tx, &new_person("X", "X"))
+    let id = authority::create_authority(&mut tx, &new_person("X", "X"))
         .await
         .unwrap();
     tx.commit().await.unwrap();
@@ -100,3 +100,28 @@ async fn resolve_authority_returns_kind(pool: PgPool) {
         .unwrap();
     assert!(missing.is_none());
 }
+
+#[sqlx::test]
+async fn authority_with_no_labels_round_trips_empty(pool: PgPool) {
+    let db = Db::from_pool(pool);
+
+    let mut tx = db.pool().begin().await.unwrap();
+    let id = authority::create_authority(
+        &mut tx,
+        &NewAuthority {
+            kind: AuthorityKind::Organisation,
+            external_uri: None,
+            labels: vec![],
+        },
+    )
+    .await
+    .unwrap();
+    tx.commit().await.unwrap();
+
+    let got = authority::authority_by_id(db.pool(), id)
+        .await
+        .unwrap()
+        .unwrap();
+    assert_eq!(got.kind, AuthorityKind::Organisation);
+    assert!(got.labels.is_empty());
+}

crates/db/tests/vocab.rs

@@ -33,7 +33,7 @@ async fn term_with_multilingual_labels_round_trips(pool: PgPool) {
 
     let mut tx = db.pool().begin().await.unwrap();
     let term_id = vocab::add_term(
-        &mut *tx,
+        &mut tx,
         &NewTerm {
             vocabulary_id: v.id,
             external_uri: Some("http://vocab.getty.edu/aat/300011914".into()),
@@ -82,7 +82,7 @@ async fn term_with_no_labels_round_trips_empty(pool: PgPool) {
 
     let mut tx = db.pool().begin().await.unwrap();
     let term_id = vocab::add_term(
-        &mut *tx,
+        &mut tx,
         &NewTerm {
             vocabulary_id: v.id,
             external_uri: None,
@@ -127,7 +127,7 @@ async fn resolve_term_checks_vocabulary_membership(pool: PgPool) {
 
     let mut tx = db.pool().begin().await.unwrap();
     let term_id = vocab::add_term(
-        &mut *tx,
+        &mut tx,
         &NewTerm {
             vocabulary_id: material.id,
             external_uri: None,