Struggling to mock trait objects and make assertions on functions that take ownership of mock trait object

[nectariner]

I'm wondering if it's possible to use mock implementation of traits as trait objects owned by a struct. I've been trying this but can't find a way of providing a mock implementation to the struct that has set return values, etc, and then can't make assertions on said trait object because of moves. Any help appreciated - thanks (I've attached some code around what I've been trying)

#[automock]
#[async_trait]
pub trait DataPuller {
    async fn get_all_books(&self) -> Result<Vec<crate::model::book::Book>, anyhow::Error>;
    async fn get_book_by_isbn(
        &self,
        isbn: &crate::model::isbn::ISBN,
    ) -> anyhow::Result<Option<crate::model::book::Book>>;
    async fn update_book_by_isbn(&self, new_book: &Book) -> anyhow::Result<()>;
    async fn insert_book(&self, new_book: &Book) -> anyhow::Result<()>;
}

--------------------------------

#[derive(Clone)]
pub struct AppState {
    pub db_client: Arc<dyn DataPuller + Send + Sync>,
}

#[derive(Clone)]
pub struct SharedState(pub Arc<RwLock<AppState>>);

impl SharedState {
    pub fn new(app_state: AppState) -> Self {
        Self(Arc::new(RwLock::new(app_state)))
    }
}

-------------------------------- test below

#[tokio::test]
async fn get_foo() {
    // mockConnect
    let puller = MockDataPuller::new();
    // How to set puller.get_all_books return value?
    let response = get(State(SharedState::new(AppState {
        db_client: Arc::new(puller),
    })))
    .await
    .unwrap();
    assert_eq!(response.0, vec![]);
    // how to assert puller.get_all_books called only once?
}

[asomers]

This is easy. Being a trait object doesn't change the way that you set expectations. Just do it like you would for any other mock object:

let mut puller = MockDataPuller::new();
puller.expect_get_all_boooks()
    .times(1)
    .returning(|| ...)

[nectariner]

Yes but this then has the type Expectation (which doesn't implement the required trait) so can't be provided to the struct containing the trait object

Also I really appreciate the quick reply

[asomers]

Obviously, don't construct AppState from the Expectation. Construct it from the Mock object.

[nectariner]

My apologies - I completely misunderstood the docs. I was doing something

let foo = MockFooImplementation::new().expect_my_function().times(1);
let my_struct = S::new(foo);

My bad!