How to mock a struct fields while unit testing?

help
#1

Hi All,

I am trying to write a test case for a function which takes in a hashmap of user structs. Inside that function, I am only using one field of the user struct. I don't have a new() or default() implemented since it is not required and I use this struct as a group of fields.

For example,

pub struct User {
    username: String,
    shortusername: String,
    longusername: String,
    address1: String,
    address2: String,
    address3: String,
    address4: String,
    contact: i32,
    active: bool
}

//Pseudo code which counts the number of items having active as true
fn count_active_users(users: HashMap<String, User>) -> usize { 
    // do something with active field 
}

Now in my testcase, I wanted to initialise only the active field. So my test case is something like below,

#[test]
fn test_count_active_users() {
    let users = HashMap::new();
    let user1 = User {active: true};
    let user2 = User {active: false};
    let user3 = User {active: true};
    users.insert("user1".tostring(), user1);
    users.insert("user2".tostring(), user2);
    users.insert("user3".tostring(), user3);
    assert_eq!(count_active_users(users), 2);
}

However, as we know, it throws compile error since the other fields are not initialised. Is it possible to set only certain field using any mock crate? Is it possible to do this with mockall?

#2

If you derive Default, you can do this:

#[derive(Default)]
pub struct User {
    username: String,
    shortusername: String,
    longusername: String,
    address1: String,
    address2: String,
    address3: String,
    address4: String,
    contact: i32,
    active: bool
}

#[test]
fn test_count_active_users() {
    let users = HashMap::new();
    let user1 = User { active: true, ..Default::default() };
    let user2 = User { active: false, ..Default::default() };
    let user3 = User { active: true, ..Default::default() };
    users.insert("user1".to_string(), user1);
    users.insert("user2".to_string(), user2);
    users.insert("user3".to_string(), user3);
    assert_eq!(count_active_users(users), 2);
}
1 Like
#3

Thanks @alice. It worked!