Mocking von Abhängigkeiten mit Thread-Lokalem Zustand

use std::cell::RefCell;
 
thread_local! {
    static MOCK_DB_RESPONSE: RefCell<Option<Result<String, &'static str>>> = const { RefCell::new(None) };
}
 
pub fn fetch_user_data(user_id: u32) -> Result<String, &'static str> {
    let mut mock_result = None;
    MOCK_DB_RESPONSE.with(|cell| {
        if let Some(ref res) = *cell.borrow() {
            mock_result = Some(res.clone());
        }
    });
 
    if let Some(result) = mock_result {
        result
    } else {
        Ok(format!("Real User Data for {}", user_id))
    }
}
 
#[cfg(test)]
mod tests {
    use super::*;
 
    #[test]
    fn test_fetch_user_data_mocked() {
        MOCK_DB_RESPONSE.with(|cell| {
            *cell.borrow_mut() = Some(Err("Database Timeout"));
        });
 
        let result = fetch_user_data(42);
        assert_eq!(result, Err("Database Timeout"));
 
        MOCK_DB_RESPONSE.with(|cell| {
            *cell.borrow_mut() = None;
        });
    }
}