code refactor

Reviewed-on: #26

crates/application/tests/users/resolve_username_to_id_test.rs

@@ -0,0 +1,20 @@
+use domain::value_objects::Username;
+
+use crate::support::TestContextBuilder;
+use application::users::deps::ResolveUsernameDeps;
+use application::users::resolve_username_to_id;
+
+#[tokio::test]
+async fn resolve_username_to_id_returns_none_for_unknown() {
+    let b = TestContextBuilder::new();
+    let deps = ResolveUsernameDeps {
+        user: b.user_repo.clone(),
+    };
+    let unknown = Username::new("nosuchuser".into()).unwrap();
+    assert!(
+        resolve_username_to_id::execute(&deps, &unknown)
+            .await
+            .unwrap()
+            .is_none()
+    );
+}