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/add_test.rs

@@ -0,0 +1,110 @@
+use crate::support::{add_to_watchlist_command, movie_input_manual};
+use domain::testing::test_movie_with_year;
+use std::sync::Arc;
+
+use domain::{
+    ports::MovieCommand,
+    testing::{InMemoryStore, NoopEventPublisher},
+};
+
+use application::watchlist::{add, commands::AddToWatchlistCommand, deps::WatchlistAddDeps};
+
+fn make_deps(movies: Arc<InMemoryStore>, watchlist: Arc<InMemoryStore>) -> WatchlistAddDeps {
+    WatchlistAddDeps {
+        movie_command: Arc::clone(&movies) as _,
+        movie_query: movies,
+        metadata: Arc::new(domain::testing::FakeMetadataClient),
+        watchlist,
+        event_publisher: NoopEventPublisher::new(),
+    }
+}
+
+#[tokio::test]
+async fn adding_to_the_watchlist_resolves_the_movie_and_saves_the_entry() {
+    let movies = InMemoryStore::new();
+    let watchlist = Arc::clone(&movies);
+
+    let movie = test_movie_with_year("The Thing", 1982);
+    let movie_uuid = movie.id().value();
+    movies.upsert_movie(&movie).await.unwrap();
+
+    let deps = make_deps(Arc::clone(&movies), Arc::clone(&watchlist));
+
+    let cmd = add_to_watchlist_command(uuid::Uuid::new_v4(), movie_uuid);
+
+    add::execute(&deps, cmd).await.unwrap();
+
+    assert_eq!(watchlist.watchlist_count(), 1);
+}
+
+#[tokio::test]
+async fn adding_a_movie_already_on_the_watchlist_is_idempotent() {
+    let movies = InMemoryStore::new();
+    let watchlist = Arc::clone(&movies);
+
+    let movie = test_movie_with_year("RoboCop", 1987);
+    let movie_uuid = movie.id().value();
+    let user_id = uuid::Uuid::new_v4();
+    movies.upsert_movie(&movie).await.unwrap();
+
+    let deps = make_deps(Arc::clone(&movies), Arc::clone(&watchlist));
+
+    let make_cmd = || add_to_watchlist_command(user_id, movie_uuid);
+
+    add::execute(&deps, make_cmd()).await.unwrap();
+    add::execute(&deps, make_cmd()).await.unwrap();
+
+    assert_eq!(
+        watchlist.watchlist_count(),
+        1,
+        "idempotent add should not duplicate"
+    );
+}
+
+#[tokio::test]
+async fn adding_a_manual_movie_to_the_watchlist_creates_and_saves_it() {
+    let movies = InMemoryStore::new();
+    let watchlist = Arc::clone(&movies);
+
+    let deps = make_deps(Arc::clone(&movies), Arc::clone(&watchlist));
+
+    let cmd = AddToWatchlistCommand {
+        user_id: uuid::Uuid::new_v4(),
+        input: movie_input_manual("New Manual Movie", 2024),
+    };
+
+    add::execute(&deps, cmd).await.unwrap();
+
+    assert_eq!(watchlist.watchlist_count(), 1);
+    assert_eq!(movies.movie_count(), 1);
+}
+
+#[tokio::test]
+async fn adding_an_unknown_movie_id_to_the_watchlist_fails() {
+    let movies = InMemoryStore::new();
+    let watchlist = Arc::clone(&movies);
+
+    let deps = make_deps(Arc::clone(&movies), Arc::clone(&watchlist));
+
+    let cmd = add_to_watchlist_command(uuid::Uuid::new_v4(), uuid::Uuid::new_v4());
+
+    assert!(add::execute(&deps, cmd).await.is_err());
+}
+
+#[tokio::test]
+async fn adding_the_same_movie_to_a_watchlist_twice_keeps_a_single_entry_and_succeeds() {
+    let movies = InMemoryStore::new();
+    let movie = test_movie_with_year("Heat", 1995);
+    let movie_uuid = movie.id().value();
+    let user_id = uuid::Uuid::new_v4();
+    movies.upsert_movie(&movie).await.unwrap();
+    let deps = make_deps(Arc::clone(&movies), Arc::clone(&movies));
+
+    for _ in 0..2 {
+        add::execute(&deps, add_to_watchlist_command(user_id, movie_uuid))
+            .await
+            .expect("second add must not error");
+    }
+
+    assert_eq!(movies.watchlist_count(), 1);
+}