diff --git a/extensions/tests/src/lib.rs b/extensions/tests/src/lib.rs
index 0e60765b9..a4cb366ec 100644
--- a/extensions/tests/src/lib.rs
+++ b/extensions/tests/src/lib.rs
@@ -1,10 +1,10 @@
 use std::cell::RefCell;
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, VecDeque};
 use std::fs::{File, OpenOptions};
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::num::NonZeroUsize;
 use std::rc::Rc;
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 use turso_ext::{
     register_extension, scalar, Connection, ConstraintInfo, ConstraintOp, ConstraintUsage,
     ExtResult, IndexInfo, OrderByInfo, ResultCode, StepResult, VTabCursor, VTabKind, VTabModule,
@@ -265,7 +265,35 @@ impl VTable for KVStoreTable {
     }
 }
 
+#[derive(Default, Clone)]
+pub struct CallbackQueue {
+    queue: Arc<Mutex<VecDeque<(Callback, i32)>>>,
+}
+
+impl CallbackQueue {
+    pub fn new() -> Self {
+        Self {
+            queue: Arc::new(Mutex::new(VecDeque::new())),
+        }
+    }
+
+    // Store a callback with its result for later execution
+    pub fn enqueue(&self, callback: Callback, result: i32) {
+        let mut queue = self.queue.lock().unwrap();
+        queue.push_back((callback, result));
+    }
+
+    // Process all pending callbacks
+    pub fn process_all(&self) {
+        let mut queue = self.queue.lock().unwrap();
+        while let Some((callback, result)) = queue.pop_front() {
+            callback(result);
+        }
+    }
+}
+
 pub struct TestFile {
+    io: CallbackQueue,
     file: File,
 }
 
@@ -274,7 +302,9 @@ pub struct TestFS;
 
 #[cfg(not(target_family = "wasm"))]
 #[derive(VfsDerive, Default)]
-pub struct TestFS;
+pub struct TestFS {
+    callbacks: CallbackQueue,
+}
 
 // Test that we can have additional extension types in the same file
 // and still register the vfs at comptime if linking staticly
@@ -287,6 +317,12 @@ fn test_scalar(_args: turso_ext::Value) -> turso_ext::Value {
 impl VfsExtension for TestFS {
     const NAME: &'static str = "testvfs";
     type File = TestFile;
+    fn run_once(&self) -> ExtResult<()> {
+        log::debug!("running once with testing VFS");
+        self.callbacks.process_all();
+        Ok(())
+    }
+
     fn open_file(&self, path: &str, flags: i32, _direct: bool) -> ExtResult<Self::File> {
         let _ = env_logger::try_init();
         log::debug!("opening file with testing VFS: {path} flags: {flags}");
@@ -296,7 +332,10 @@ impl VfsExtension for TestFS {
             .create(flags & 1 != 0)
             .open(path)
             .map_err(|_| ResultCode::Error)?;
-        Ok(TestFile { file })
+        Ok(TestFile {
+            file,
+            io: self.callbacks.clone(),
+        })
     }
 }
 
@@ -318,7 +357,7 @@ impl VfsFile for TestFile {
             .read(&mut buf[..len])
             .map_err(|_| ResultCode::Error)
             .map(|n| n as i32)?;
-        cb(res as i32);
+        self.io.enqueue(cb, res);
         Ok(())
     }
 
@@ -336,14 +375,14 @@ impl VfsFile for TestFile {
             .write(&buf[..len])
             .map_err(|_| ResultCode::Error)
             .map(|n| n as i32)?;
-        cb(n as i32);
+        self.io.enqueue(cb, n);
         Ok(())
     }
 
     fn sync(&self, cb: Callback) -> ExtResult<()> {
         log::debug!("syncing file with testing VFS");
         self.file.sync_all().map_err(|_| ResultCode::Error)?;
-        cb(0);
+        self.io.enqueue(cb, 0);
         Ok(())
     }
 
@@ -352,7 +391,7 @@ impl VfsFile for TestFile {
         self.file
             .set_len(len as u64)
             .map_err(|_| ResultCode::Error)?;
-        cb(0);
+        self.io.enqueue(cb, 0);
         Ok(())
     }