test: move application tests to tests/

test_support/test_helpers -> tests/support; watched_at unified w/ domain test_watched_at (2024-03-15).
Kept inline: users::diary_filter tests (feed_sort_to_direction_all_variants, paged_user_filter_builds_correctly) - pub(super) helpers in private module.
Dropped stale never-compiled users/tests/get_users.rs (old execute signature).

crates/application/tests/watchlist/is_on_test.rs

@@ -0,0 +1,58 @@
+use std::sync::Arc;
+
+use domain::models::WatchlistEntry;
+use domain::ports::WatchlistRepository;
+use domain::testing::InMemoryStore;
+use domain::value_objects::{MovieId, UserId};
+use uuid::Uuid;
+
+use crate::support::TestContextBuilder;
+use application::watchlist::{deps::IsOnWatchlistDeps, is_on, queries::IsOnWatchlistQuery};
+
+#[tokio::test]
+async fn returns_true_when_present() {
+    let watchlist = InMemoryStore::new();
+    let uid = Uuid::new_v4();
+    let mid = Uuid::new_v4();
+    watchlist
+        .add(&WatchlistEntry::new(
+            UserId::from_uuid(uid),
+            MovieId::from_uuid(mid),
+        ))
+        .await
+        .unwrap();
+
+    let deps = IsOnWatchlistDeps {
+        watchlist: Arc::clone(&watchlist) as _,
+    };
+    let result = is_on::execute(
+        &deps,
+        IsOnWatchlistQuery {
+            user_id: uid,
+            movie_id: mid,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(result);
+}
+
+#[tokio::test]
+async fn returns_false_when_absent() {
+    let b = TestContextBuilder::new();
+    let deps = IsOnWatchlistDeps {
+        watchlist: b.watchlist_repo.clone(),
+    };
+    let result = is_on::execute(
+        &deps,
+        IsOnWatchlistQuery {
+            user_id: Uuid::new_v4(),
+            movie_id: Uuid::new_v4(),
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(!result);
+}