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/get_test.rs

@@ -0,0 +1,25 @@
+use uuid::Uuid;
+
+use crate::support::TestContextBuilder;
+use application::watchlist::{deps::GetWatchlistDeps, get, queries::GetWatchlistQuery};
+
+#[tokio::test]
+async fn returns_empty_page_for_new_user() {
+    let b = TestContextBuilder::new();
+    let deps = GetWatchlistDeps {
+        watchlist: b.watchlist_repo.clone(),
+    };
+    let result = get::execute(
+        &deps,
+        GetWatchlistQuery {
+            user_id: Uuid::new_v4(),
+            limit: None,
+            offset: None,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(result.items.is_empty());
+    assert_eq!(result.total_count, 0);
+}