Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

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

crates/collab/src/db/tests/buffer_tests.rs

@@ -0,0 +1,41 @@
+use super::*;
+use crate::test_both_dbs;
+use language::proto;
+use text::Buffer;
+
+test_both_dbs!(test_buffers, test_buffers_postgres, test_buffers_sqlite);
+
+async fn test_buffers(db: &Arc<Database>) {
+    let buffer_id = db.create_buffer().await.unwrap();
+
+    let mut buffer = Buffer::new(0, 0, "".to_string());
+    let mut operations = Vec::new();
+    operations.push(buffer.edit([(0..0, "hello world")]));
+    operations.push(buffer.edit([(5..5, ", cruel")]));
+    operations.push(buffer.edit([(0..5, "goodbye")]));
+    operations.push(buffer.undo().unwrap().1);
+    assert_eq!(buffer.text(), "hello, cruel world");
+
+    let operations = operations
+        .into_iter()
+        .map(|op| proto::serialize_operation(&language::Operation::Buffer(op)))
+        .collect::<Vec<_>>();
+
+    db.update_buffer(buffer_id, &operations).await.unwrap();
+
+    let buffer_data = db.get_buffer(buffer_id).await.unwrap();
+
+    let mut buffer_2 = Buffer::new(0, 0, buffer_data.base_text);
+    buffer_2
+        .apply_ops(buffer_data.operations.into_iter().map(|operation| {
+            let operation = proto::deserialize_operation(operation).unwrap();
+            if let language::Operation::Buffer(operation) = operation {
+                operation
+            } else {
+                unreachable!()
+            }
+        }))
+        .unwrap();
+
+    assert_eq!(buffer_2.text(), "hello, cruel world");
+}