docs: add docstrings to list_user_courses.rs

contracts/course/course_access/src/functions/list_user_courses.rs

@@ -5,7 +5,21 @@ use soroban_sdk::{Address, Env, Vec};
 
 use crate::schema::{DataKey, UserCourses};
 
-
+/// Retrieves the list of courses associated with a specific user.
+///
+/// This function queries the persistent storage to fetch all courses 
+/// that the specified user has access to. If no courses are found for
+/// the user, it returns an empty `UserCourses` struct.
+///
+/// # Arguments
+///
+/// * `env` - The Soroban environment context for accessing storage and other SDK features.
+/// * `user` - The blockchain address of the user whose courses are being retrieved.
+///
+/// # Returns
+///
+/// * `UserCourses` - A struct containing the user's address and a vector of their course IDs.
+///   If the user has no courses, returns a `UserCourses` with an empty courses vector.
 pub fn list_user_courses(env: Env, user: Address) -> UserCourses {
     let key: DataKey = DataKey::UserCourses(user.clone());
     let res: UserCourses = env.storage().persistent().get(&key).unwrap_or(UserCourses {
@@ -23,6 +37,11 @@ mod test {
     use soroban_sdk::{testutils::Address as _, vec, Address, Env, String};
     use super::list_user_courses;
 
+    /// Tests the `list_user_courses` function to verify correct retrieval of user courses.
+    ///
+    /// This test sets up a mock environment with a registered contract and user,
+    /// creates course data, stores it in persistent storage, and verifies that
+    /// `list_user_courses` correctly retrieves the stored data.
     #[test]
     fn test_list_user_courses() {
         let env: Env = Env::default();