1use gpui::{Entity, ModelHandle};
 2use smol::channel;
 3use std::marker::PhantomData;
 4
 5pub fn sample_text(rows: usize, cols: usize) -> String {
 6    let mut text = String::new();
 7    for row in 0..rows {
 8        let c: char = ('a' as u32 + row as u32) as u8 as char;
 9        let mut line = c.to_string().repeat(cols);
10        if row < rows - 1 {
11            line.push('\n');
12        }
13        text += &line;
14    }
15    text
16}
17
18pub struct Observer<T>(PhantomData<T>);
19
20impl<T: 'static> Entity for Observer<T> {
21    type Event = ();
22}
23
24impl<T: Entity> Observer<T> {
25    pub fn new(
26        handle: &ModelHandle<T>,
27        cx: &mut gpui::TestAppContext,
28    ) -> (ModelHandle<Self>, channel::Receiver<()>) {
29        let (notify_tx, notify_rx) = channel::unbounded();
30        let observer = cx.add_model(|cx| {
31            cx.observe(handle, move |_, _, _| {
32                let _ = notify_tx.try_send(());
33            })
34            .detach();
35            Observer(PhantomData)
36        });
37        (observer, notify_rx)
38    }
39}