diff --git a/crate/memory/src/swap/mock_swapper.rs b/crate/memory/src/swap/mock_swapper.rs
new file mode 100644
index 0000000..af8d8ba
--- /dev/null
+++ b/crate/memory/src/swap/mock_swapper.rs
@@ -0,0 +1,53 @@
+use super::Swapper;
+use alloc::btree_map::BTreeMap;
+
+pub struct MockSwapper {
+    map: BTreeMap<usize, [u8; 4096]>,
+}
+
+impl Swapper for MockSwapper {
+    fn swap_out(&mut self, data: &[u8; 4096]) -> usize {
+        let id = self.alloc_id();
+        self.map.insert(id, data.clone());
+        id
+    }
+
+    fn swap_in(&mut self, token: usize, data: &mut [u8; 4096]) {
+        *data = self.map.remove(&token).unwrap();
+    }
+}
+
+impl MockSwapper {
+    pub fn new() -> Self {
+        MockSwapper {map: BTreeMap::new()}
+    }
+    fn alloc_id(&self) -> usize {
+        (0 .. 100usize).find(|i| !self.map.contains_key(i)).unwrap()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use core::mem::uninitialized;
+
+    #[test]
+    fn test() {
+        let mut swapper = MockSwapper::new();
+        let data: [u8; 4096] = unsafe{ uninitialized() };
+        let mut data1: [u8; 4096] = unsafe{ uninitialized() };
+        let token = swapper.swap_out(&data);
+        swapper.swap_in(token, &mut data1);
+        for (&a, &b) in data.iter().zip(data1.iter()) {
+            assert_eq!(a, b);
+        }
+    }
+
+    #[test]
+    #[should_panic]
+    fn invalid_token() {
+        let mut swapper = MockSwapper::new();
+        let mut data: [u8; 4096] = unsafe{ uninitialized() };
+        swapper.swap_in(0, &mut data);
+    }
+}
\ No newline at end of file
diff --git a/crate/memory/src/swap/mod.rs b/crate/memory/src/swap/mod.rs
index 80b1e5a..214779c 100644
--- a/crate/memory/src/swap/mod.rs
+++ b/crate/memory/src/swap/mod.rs
@@ -1,5 +1,6 @@
 pub mod fifo;
 mod mock_page_table;
+mod mock_swapper;
 
 type Addr = usize;
 
@@ -19,4 +20,9 @@ trait SwapManager<T: PageTable> {
 trait PageTable {
     fn accessed(&self, addr: Addr) -> bool;
     fn dirty(&self, addr: Addr) -> bool;
+}
+
+trait Swapper {
+    fn swap_out(&mut self, data: &[u8; 4096]) -> usize;
+    fn swap_in(&mut self, token: usize, data: &mut [u8; 4096]);
 }
\ No newline at end of file