diff --git a/kernel/src/objects/untyped.rs b/kernel/src/objects/untyped.rs
index 89d7ef0..ae32717 100644
--- a/kernel/src/objects/untyped.rs
+++ b/kernel/src/objects/untyped.rs
@@ -130,3 +130,100 @@ impl UntypedCap<'_> {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{arch::vspace::KERNEL_ALLOCATOR, objects::cap::CapEntry};
+    use core::alloc::Layout;
+    use log::info;
+
+    fn alloc_mem(size: usize) -> PhysAddr {
+        assert!(size.is_power_of_two());
+        let layout = Layout::from_size_align(size, 1).unwrap();
+        KERNEL_ALLOCATOR.lock().alloc(layout).unwrap()
+    }
+
+    fn create_untyped_cte(size: usize, is_device: bool) -> CapEntry {
+        let ptr = alloc_mem(size);
+        let raw = UntypedCap::mint(0, size.ilog2() as usize, is_device, ptr);
+        CapEntry::new(raw)
+    }
+
+    fn create_cnode_cte(size: usize, guard_size: usize, guard: usize) -> CapEntry {
+        let ptr = alloc_mem(size);
+        let radix = size.ilog2() as usize - ObjectType::CNode.bits(0);
+        let raw = CNodeCap::mint(radix, guard_size, guard, ptr);
+        CapEntry::new(raw)
+    }
+
+    #[test_case]
+    fn test_untyped_retype_cnode() {
+        // create untyped
+        let untyped_cte = create_untyped_cte(4 * ObjectType::CNode.size(2), false); // 4 cnode (4 entries each)
+        let mut untyped = UntypedCap::try_from(&untyped_cte).unwrap();
+
+        // create root cnode
+        let cnode_cte = create_cnode_cte(ObjectType::CNode.size(4), 3, 0b110); // 1 cnode (16 entries)
+        let mut cnode = CNodeCap::try_from(&cnode_cte).unwrap();
+
+        // slots
+        let slots = cnode.as_object_mut();
+
+        // retype untyped to cnode
+        info!("Retyping to ObjectType::CNode");
+        untyped.retype(ObjectType::CNode, 2, &mut slots[1..2]).unwrap();
+        untyped.retype(ObjectType::CNode, 2, &mut slots[9..12]).unwrap();
+
+        // check untyped
+        info!("Checking remain space in untyped");
+        assert_eq!(untyped.free_offset(), untyped.block_size());
+        assert!(untyped.retype(ObjectType::CNode, 1, &mut slots[0..1]).is_err());
+
+        // check cnode
+        info!("Checking retyped cnode length");
+        for addr in [1, 9, 10, 11] {
+            let cte = cnode.resolve_address_bits(0b110_0000 | addr, 7).unwrap();
+            let cap = CNodeCap::try_from(cte).unwrap();
+            let len = cap.as_object().len();
+            assert_eq!(len, 4);
+        }
+        info!("Make sure other cnodes are not modified");
+        for addr in 0..16 {
+            if [1, 9, 10, 11].contains(&addr) {
+                continue;
+            }
+            let cte = cnode.resolve_address_bits(0b110_0000 | addr, 7).unwrap();
+            NullCap::try_from(cte).unwrap();
+        }
+    }
+
+    #[test_case]
+    fn test_untyped_retype_device_err() {
+        // create untyped
+        let untyped_cte = create_untyped_cte(ObjectType::CNode.size(1), true);
+        let mut untyped = UntypedCap::try_from(&untyped_cte).unwrap();
+
+        // create root cnode
+        let cnode_cte = create_cnode_cte(ObjectType::CNode.size(1), 3, 0b110);
+        let mut cnode = CNodeCap::try_from(&cnode_cte).unwrap();
+
+        // slots
+        let slots = cnode.as_object_mut();
+
+        // allocate fail
+        info!("Retyping to ObjectType::CNode with device memory");
+        untyped
+            .retype(ObjectType::CNode, 1, &mut slots[0..1])
+            .is_err()
+            .then_ok((), ())
+            .unwrap();
+
+        // nothing should be changed
+        info!("Make sure nothing is changed");
+        assert_eq!(untyped.free_offset(), 0);
+        NullCap::try_from(&slots[0]).unwrap();
+    }
+
+    // TODO: more tests
+}