Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

co-authored-by: Max <max@zed.dev>

crates/collab/src/tests/channel_buffer_tests.rs

@@ -0,0 +1,84 @@
+use crate::tests::TestServer;
+
+use channel::channel_buffer::ChannelBuffer;
+use gpui::{executor::Deterministic, ModelHandle, TestAppContext};
+use std::{ops::Range, sync::Arc};
+
+#[gpui::test]
+async fn test_channel_buffers(
+    deterministic: Arc<Deterministic>,
+    cx_a: &mut TestAppContext,
+    cx_b: &mut TestAppContext,
+) {
+    deterministic.forbid_parking();
+    let mut server = TestServer::start(&deterministic).await;
+    let client_a = server.create_client(cx_a, "user_a").await;
+    let client_b = server.create_client(cx_b, "user_b").await;
+
+    let zed_id = server
+        .make_channel("zed", (&client_a, cx_a), &mut [(&client_b, cx_b)])
+        .await;
+
+    let a_document =
+        cx_a.add_model(|cx| ChannelBuffer::for_channel(zed_id, client_a.client().to_owned(), cx));
+    let channel_buffer_a = a_document
+        .update(cx_a, |doc, cx| doc.buffer(cx))
+        .await
+        .unwrap();
+
+    edit_channel_buffer(&channel_buffer_a, cx_a, [(0..0, "hello world")]);
+    edit_channel_buffer(&channel_buffer_a, cx_a, [(5..5, ", cruel")]);
+    edit_channel_buffer(&channel_buffer_a, cx_a, [(0..5, "goodbye")]);
+    undo_channel_buffer(&channel_buffer_a, cx_a);
+
+    assert_eq!(
+        channel_buffer_text(&channel_buffer_a, cx_a),
+        "hello, cruel world"
+    );
+
+    let b_document =
+        cx_b.add_model(|cx| ChannelBuffer::for_channel(zed_id, client_b.client().to_owned(), cx));
+    let channel_buffer_b = b_document
+        .update(cx_b, |doc, cx| doc.buffer(cx))
+        .await
+        .unwrap();
+
+    assert_eq!(
+        channel_buffer_text(&channel_buffer_b, cx_b),
+        "hello, cruel world"
+    );
+
+    edit_channel_buffer(&channel_buffer_b, cx_b, [(7..12, "beautiful")]);
+
+    deterministic.run_until_parked();
+
+    assert_eq!(
+        channel_buffer_text(&channel_buffer_a, cx_a),
+        "hello, beautiful world"
+    );
+    assert_eq!(
+        channel_buffer_text(&channel_buffer_b, cx_b),
+        "hello, beautiful world"
+    );
+}
+
+fn edit_channel_buffer<I>(
+    channel_buffer: &ModelHandle<language::Buffer>,
+    cx: &mut TestAppContext,
+    edits: I,
+) where
+    I: IntoIterator<Item = (Range<usize>, &'static str)>,
+{
+    channel_buffer.update(cx, |buffer, cx| buffer.edit(edits, None, cx));
+}
+
+fn undo_channel_buffer(channel_buffer: &ModelHandle<language::Buffer>, cx: &mut TestAppContext) {
+    channel_buffer.update(cx, |buffer, cx| buffer.undo(cx));
+}
+
+fn channel_buffer_text(
+    channel_buffer: &ModelHandle<language::Buffer>,
+    cx: &mut TestAppContext,
+) -> String {
+    channel_buffer.read_with(cx, |buffer, _| buffer.text())
+}