feat(api+testing): select todo by member_id and id

- Added test code coverage with `pytest-cov`
- Added comments for member model functions

backend/tests/test_model_todo.py

@@ -1,4 +1,6 @@
-from src.neo_neo_todo.models.todo import select_todos
+import asyncio
+
+from src.neo_neo_todo.models.todo import select_todo, select_todos
 
 
 async def test_model_todo_select_todos(db_pool):
@@ -17,3 +19,23 @@ async def test_model_todo_select_todos(db_pool):
     todos_list_non_existent_member_id = await select_todos(db_pool, 12341234)
 
     assert len(todos_list_non_existent_member_id) == 0
+
+
+async def test_model_todo_select_todo(db_pool):
+    todo_queries = [
+        select_todo(db_pool, member_id=1, id=1),
+        select_todo(db_pool, member_id=1, id=2),
+        select_todo(db_pool, member_id=1, id=3),
+    ]
+
+    # Now you can await all the select_todo calls
+    todos = await asyncio.gather(*todo_queries)
+
+    for i in range(len(todos)):
+        assert todos[i] is not None
+        assert todos[i].id == (i + 1)  # type: ignore
+        assert not todos[i].complete  # type: ignore
+
+    non_existent_member_id_todo = await select_todo(db_pool, member_id=1234123, id=1)
+
+    assert non_existent_member_id_todo is None