diff --git a/crates/oxide_types/src/object.rs b/crates/oxide_types/src/object.rs
index 766d10a8..88f2b731 100644
--- a/crates/oxide_types/src/object.rs
+++ b/crates/oxide_types/src/object.rs
@@ -2133,315 +2133,4 @@ impl JsObject {
 }
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::shape::EMPTY_SHAPE_ID;
-
-    #[test]
-    fn object_size_bounds() {
-        let sz = std::mem::size_of::<JsObject>();
-        assert!(sz <= 256, "JsObject grew unexpectedly: {sz}B");
-    }
-
-    #[test]
-    fn js_string_cons_basic() {
-        // 左右子 Flat 构造 Cons：utf16_len/is_empty/文本视图全部按拼接语义。
-        let left = Box::new(JsString::new("ab".to_string()));
-        let right = Box::new(JsString::new("cd".to_string()));
-        let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
-        assert_eq!(cons.utf16_len(), 4);
-        assert!(!cons.is_empty());
-        assert_eq!(cons.as_lossy_str(), "abcd");
-        assert_eq!(cons.to_owned_string(), "abcd");
-        assert!(cons.is_cons());
-        // 扁平化产物缓存命中：内容仍一致（units 视图同样走缓存）。
-        assert_eq!(cons.as_lossy_str(), "abcd");
-        assert_eq!(cons.units().as_ref(), &['a' as u16, 'b' as u16, 'c' as u16, 'd' as u16]);
-    }
-
-    #[test]
-    fn js_string_layout_anchor_and_tags() {
-        // 32B 锚 + 三形态 tag/utf16_len 预写口径（布局变更先同步头注释再改断言）。
-        let flat = JsString::new("ab".to_string());
-        assert_eq!(std::mem::size_of::<JsString>(), 32);
-        assert!(flat.is_flat() && !flat.is_cons() && !flat.is_flat_u16());
-        assert_eq!(flat.tag, TAG_FLAT);
-        assert_eq!(flat.utf16_len(), 2);
-        assert_eq!(flat.payload_bytes(), 2);
-
-        let u16 = JsString::new_flat_u16(vec![0xD800, 0xDC00]);
-        assert!(u16.is_flat_u16());
-        assert_eq!(u16.tag, TAG_FLAT_U16);
-        assert_eq!(u16.utf16_len(), 2);
-        assert_eq!(u16.payload_bytes(), 4);
-        assert_eq!(u16.units_borrowed(), Some(&[0xD800, 0xDC00][..]));
-        // 代理对 well-formed：smart 路由落 Flat 且内容等价。
-        let smart = JsString::from_units(vec![0xD800, 0xDC00]);
-        assert!(smart.is_flat());
-        assert_eq!(smart.as_str(), "\u{10000}");
-        // 孤立 surrogate：smart 路由落 FlatU16。
-        let lone = JsString::from_units(vec![0xD800]);
-        assert!(lone.is_flat_u16());
-        assert!(lone.has_lone_surrogate());
-        assert_eq!(lone.units().as_ref(), &[0xD800]);
-        assert_eq!(lone.as_lossy_str(), "\u{FFFD}");
-
-        let left = Box::new(JsString::new("ab".to_string()));
-        let right = Box::new(JsString::new("cd".to_string()));
-        let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
-        assert!(cons.is_cons());
-        assert_eq!(cons.tag, TAG_CONS);
-        assert_eq!(cons.utf16_len(), 4, "Cons 单元长构造期 eager 归纳");
-        assert_eq!(cons.payload_bytes(), 8);
-        assert!(!cons.has_lone_surrogate());
-        // Cons 扁平化产物恒 FlatU16：units 零拷贝借用来自缓存。
-        let u16_node = cons.units().into_owned();
-        assert_eq!(u16_node, vec![0x61, 0x62, 0x63, 0x64]);
-        assert!(!cons.flat_cache_ptr().is_null());
-        unsafe { JsString::drop_cons_node(cons.cons_node_ptr()) };
-    }
-
-    #[test]
-    fn js_string_cons_deep_chain_flattens_iteratively() {
-        // 2000 层左倾链：显式栈展开不爆栈，产物与逐段拼接一致。
-        let mut nodes: Vec<Box<JsString>> = Vec::new();
-        nodes.push(Box::new(JsString::new("x".to_string())));
-        for _ in 0..2000 {
-            nodes.push(Box::new(JsString::new("y".to_string())));
-        }
-        let mut chain_ptr = nodes[0].as_ref() as *const JsString;
-        for i in 1..nodes.len() {
-            let cons = Box::new(unsafe { JsString::new_cons(chain_ptr, nodes[i].as_ref() as *const JsString) });
-            chain_ptr = cons.as_ref() as *const JsString;
-            nodes.push(cons);
-        }
-        let text = nodes.last().unwrap().as_lossy_str();
-        assert_eq!(text.len(), 1 + 2000);
-        assert!(text.starts_with('x'));
-        assert!(text.ends_with('y'));
-    }
-
-    #[test]
-    fn js_string_cons_empty_parts() {
-        // 双空串 Cons：空判定与长度均为 0，扁平化为空文本。
-        let left = Box::new(JsString::new(String::new()));
-        let right = Box::new(JsString::new(String::new()));
-        let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
-        assert!(cons.is_empty());
-        assert_eq!(cons.utf16_len(), 0);
-        assert_eq!(cons.as_lossy_str(), "");
-    }
-
-    #[test]
-    fn new_empty_defaults() {
-        let obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert_eq!(obj.shape_id(), EMPTY_SHAPE_ID);
-        assert_eq!(obj.prop_count(), 0);
-        assert!(obj.is_extensible());
-        assert!(!obj.is_array());
-        assert!(!obj.is_function());
-        assert!(!obj.is_session_epoch());
-        assert_eq!(obj.generation(), 1);
-        assert!(obj.hash_props_vec().is_none());
-        assert!(!obj.has_prop_meta());
-    }
-
-    #[test]
-    fn session_epoch_marker_roundtrip() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert!(!obj.is_session_epoch());
-        obj.set_session_epoch(true);
-        assert!(obj.is_session_epoch());
-        obj.set_session_epoch(false);
-        assert!(!obj.is_session_epoch());
-    }
-
-    #[test]
-    fn session_epoch_marker_preserves_gc_mark_bit() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert!(!obj.is_gc_marked());
-        obj.set_gc_mark(true);
-        assert!(obj.is_gc_marked());
-        assert!(!obj.is_session_epoch());
-
-        obj.set_session_epoch(true);
-        assert!(obj.is_session_epoch());
-        assert!(obj.is_gc_marked());
-
-        obj.set_gc_mark(false);
-        assert!(!obj.is_gc_marked());
-    }
-
-    #[test]
-    fn session_epoch_marker_keeps_object_size_bound() {
-        let sz = std::mem::size_of::<JsObject>();
-        assert!(sz <= 256, "JsObject grew unexpectedly: {sz}B");
-    }
-
-    #[test]
-    fn clone_for_session_epoch_marks_clone_and_does_not_alias_hash_props() {
-        let mut source = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        source.set_prop_at(0, JsValue::int(1));
-
-        let mut clone = source.clone_for_session_epoch();
-        assert!(clone.is_session_epoch());
-        clone.set_prop_at(0, JsValue::int(2));
-
-        assert_eq!(source.get_prop_at(0), JsValue::int(1));
-        assert_eq!(clone.get_prop_at(0), JsValue::int(2));
-    }
-
-    #[test]
-    fn clone_for_session_epoch_does_not_alias_prop_meta() {
-        let mut source = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        source.set_prop_at(0, JsValue::undefined());
-        source.set_accessor_meta(0, JsValue::int(10), JsValue::int(11), PropAttributes::DEFAULT_DATA);
-
-        let mut clone = source.clone_for_session_epoch();
-        clone.set_accessor_meta(0, JsValue::int(20), JsValue::int(21), PropAttributes::DEFAULT_DATA);
-
-        let source_meta = source.prop_meta_at(0).expect("source meta");
-        let clone_meta = clone.prop_meta_at(0).expect("clone meta");
-        assert_eq!(source_meta.get, JsValue::int(10));
-        assert_eq!(source_meta.set, JsValue::int(11));
-        assert_eq!(clone_meta.get, JsValue::int(20));
-        assert_eq!(clone_meta.set, JsValue::int(21));
-    }
-
-    #[test]
-    fn shape_id_roundtrip() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        obj.set_shape_id(0x00AB_CDEF);
-        assert_eq!(obj.shape_id(), 0x00AB_CDEF);
-    }
-
-    #[test]
-    fn prop_count_roundtrip() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert_eq!(obj.prop_count(), 0);
-        obj.ensure_hash_props().push(JsValue::int(17));
-        assert_eq!(obj.prop_count(), 1);
-    }
-
-    #[test]
-    fn flags_individual() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert!(obj.is_extensible());
-        obj.set_extensible(false);
-        assert!(!obj.is_extensible());
-    }
-
-    #[test]
-    fn hash_prop_read_write() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        obj.set_prop_at(0, JsValue::int(42));
-        assert_eq!(obj.get_prop_at(0), JsValue::int(42));
-    }
-
-    #[test]
-    fn new_array_flags() {
-        let bump = bumpalo::Bump::new();
-        let obj = JsObject::new_array(5, JsValue::null(), 3, &bump);
-        assert!(obj.is_array());
-        assert_eq!(obj.shape_id(), 5);
-        assert_eq!(obj.prop_count(), 3);
-    }
-
-    #[test]
-    fn generation_bump() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert_eq!(obj.generation(), 1);
-        obj.bump_generation();
-        assert_eq!(obj.generation(), 2);
-    }
-
-    #[test]
-    fn hash_props_lazy_init() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        assert!(obj.hash_props_vec().is_none());
-        assert_eq!(obj.prop_count(), 0);
-        obj.set_prop_at(0, JsValue::int(1));
-        assert!(obj.hash_props_vec().is_some());
-        assert_eq!(obj.prop_count(), 1);
-    }
-
-    #[test]
-    fn hash_props_flat_storage_roundtrip() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        obj.set_prop_at(0, JsValue::int(100));
-        obj.set_prop_at(1, JsValue::int(200));
-        assert_eq!(obj.get_prop_at(0), JsValue::int(100));
-        assert_eq!(obj.get_prop_at(1), JsValue::int(200));
-    }
-
-    #[test]
-    fn prop_meta_lazy_init() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        obj.set_prop_at(0, JsValue::int(1));
-        assert!(!obj.has_prop_meta());
-
-        obj.set_data_meta(0, PropAttributes::new(false, true, false));
-        assert!(obj.has_prop_meta());
-        let meta = obj.prop_meta_at(0).expect("meta");
-        assert!(!meta.is_accessor);
-        assert!(!meta.attributes.writable());
-        assert!(meta.attributes.enumerable());
-        assert!(!meta.attributes.configurable());
-    }
-
-    #[test]
-    fn accessor_meta_roundtrip_and_alignment() {
-        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
-        obj.set_prop_at(0, JsValue::int(1));
-        obj.set_accessor_meta(2, JsValue::int(10), JsValue::int(11), PropAttributes::new(false, false, true));
-
-        assert_eq!(obj.prop_count(), 3);
-        assert!(obj.is_accessor_meta(2));
-        let meta = obj.prop_meta_at(2).expect("accessor meta");
-        assert_eq!(meta.get, JsValue::int(10));
-        assert_eq!(meta.set, JsValue::int(11));
-        assert!(!meta.attributes.writable());
-        assert!(!meta.attributes.enumerable());
-        assert!(meta.attributes.configurable());
-
-        obj.push_prop(JsValue::int(4));
-        assert_eq!(obj.prop_meta_vec().expect("meta").len(), obj.prop_vec_len());
-    }
-
-    #[test]
-    fn array_element_write_preserves_props_after_element_growth() {
-        // 先写属性再 push 元素：元素区增长必须整体搬移属性区，不覆盖属性。
-        let bump = bumpalo::Bump::new();
-        let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 3, &bump);
-        obj.set_prop_shape(0, JsValue::int(99));
-        obj.set_prop_at(3, JsValue::int(4));
-        assert_eq!(obj.prop_count(), 4);
-        assert_eq!(obj.get_prop_at(3), JsValue::int(4));
-        assert_eq!(obj.get_prop_shape(0), JsValue::int(99));
-    }
-
-    #[test]
-    fn array_element_write_beyond_count_relocates_prop_zone() {
-        // 稀疏写入（越界索引）把属性区推到新元素之后，属性读取仍命中。
-        let bump = bumpalo::Bump::new();
-        let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 2, &bump);
-        obj.set_prop_shape(0, JsValue::int(7));
-        obj.set_prop_at(5, JsValue::int(50));
-        assert_eq!(obj.prop_count(), 6);
-        assert_eq!(obj.get_prop_at(5), JsValue::int(50));
-        assert_eq!(obj.get_prop_shape(0), JsValue::int(7));
-    }
-
-    #[test]
-    fn array_prop_count_truncate_keeps_prop_zone() {
-        // pop 截断元素区时属性区不得被删（meta 同步 insert/drain 对齐）。
-        let bump = bumpalo::Bump::new();
-        let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 3, &bump);
-        obj.set_prop_shape(0, JsValue::int(5));
-        obj.set_data_meta(3, PropAttributes::new(true, false, true));
-        obj.set_prop_count_fast(2);
-        assert_eq!(obj.prop_count(), 2);
-        assert_eq!(obj.get_prop_shape(0), JsValue::int(5));
-        assert!(obj.prop_meta_at(2).is_some());
-    }
-}
+mod tests;
diff --git a/crates/oxide_types/src/object/tests.rs b/crates/oxide_types/src/object/tests.rs
new file mode 100644
index 00000000..ca4463f7
--- /dev/null
+++ b/crates/oxide_types/src/object/tests.rs
@@ -0,0 +1,310 @@
+use super::*;
+use crate::shape::EMPTY_SHAPE_ID;
+
+#[test]
+fn object_size_bounds() {
+    let sz = std::mem::size_of::<JsObject>();
+    assert!(sz <= 256, "JsObject grew unexpectedly: {sz}B");
+}
+
+#[test]
+fn js_string_cons_basic() {
+    // 左右子 Flat 构造 Cons：utf16_len/is_empty/文本视图全部按拼接语义。
+    let left = Box::new(JsString::new("ab".to_string()));
+    let right = Box::new(JsString::new("cd".to_string()));
+    let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
+    assert_eq!(cons.utf16_len(), 4);
+    assert!(!cons.is_empty());
+    assert_eq!(cons.as_lossy_str(), "abcd");
+    assert_eq!(cons.to_owned_string(), "abcd");
+    assert!(cons.is_cons());
+    // 扁平化产物缓存命中：内容仍一致（units 视图同样走缓存）。
+    assert_eq!(cons.as_lossy_str(), "abcd");
+    assert_eq!(cons.units().as_ref(), &['a' as u16, 'b' as u16, 'c' as u16, 'd' as u16]);
+}
+
+#[test]
+fn js_string_layout_anchor_and_tags() {
+    // 32B 锚 + 三形态 tag/utf16_len 预写口径（布局变更先同步头注释再改断言）。
+    let flat = JsString::new("ab".to_string());
+    assert_eq!(std::mem::size_of::<JsString>(), 32);
+    assert!(flat.is_flat() && !flat.is_cons() && !flat.is_flat_u16());
+    assert_eq!(flat.tag, TAG_FLAT);
+    assert_eq!(flat.utf16_len(), 2);
+    assert_eq!(flat.payload_bytes(), 2);
+
+    let u16 = JsString::new_flat_u16(vec![0xD800, 0xDC00]);
+    assert!(u16.is_flat_u16());
+    assert_eq!(u16.tag, TAG_FLAT_U16);
+    assert_eq!(u16.utf16_len(), 2);
+    assert_eq!(u16.payload_bytes(), 4);
+    assert_eq!(u16.units_borrowed(), Some(&[0xD800, 0xDC00][..]));
+    // 代理对 well-formed：smart 路由落 Flat 且内容等价。
+    let smart = JsString::from_units(vec![0xD800, 0xDC00]);
+    assert!(smart.is_flat());
+    assert_eq!(smart.as_str(), "\u{10000}");
+    // 孤立 surrogate：smart 路由落 FlatU16。
+    let lone = JsString::from_units(vec![0xD800]);
+    assert!(lone.is_flat_u16());
+    assert!(lone.has_lone_surrogate());
+    assert_eq!(lone.units().as_ref(), &[0xD800]);
+    assert_eq!(lone.as_lossy_str(), "\u{FFFD}");
+
+    let left = Box::new(JsString::new("ab".to_string()));
+    let right = Box::new(JsString::new("cd".to_string()));
+    let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
+    assert!(cons.is_cons());
+    assert_eq!(cons.tag, TAG_CONS);
+    assert_eq!(cons.utf16_len(), 4, "Cons 单元长构造期 eager 归纳");
+    assert_eq!(cons.payload_bytes(), 8);
+    assert!(!cons.has_lone_surrogate());
+    // Cons 扁平化产物恒 FlatU16：units 零拷贝借用来自缓存。
+    let u16_node = cons.units().into_owned();
+    assert_eq!(u16_node, vec![0x61, 0x62, 0x63, 0x64]);
+    assert!(!cons.flat_cache_ptr().is_null());
+    unsafe { JsString::drop_cons_node(cons.cons_node_ptr()) };
+}
+
+#[test]
+fn js_string_cons_deep_chain_flattens_iteratively() {
+    // 2000 层左倾链：显式栈展开不爆栈，产物与逐段拼接一致。
+    let mut nodes: Vec<Box<JsString>> = Vec::new();
+    nodes.push(Box::new(JsString::new("x".to_string())));
+    for _ in 0..2000 {
+        nodes.push(Box::new(JsString::new("y".to_string())));
+    }
+    let mut chain_ptr = nodes[0].as_ref() as *const JsString;
+    for i in 1..nodes.len() {
+        let cons = Box::new(unsafe { JsString::new_cons(chain_ptr, nodes[i].as_ref() as *const JsString) });
+        chain_ptr = cons.as_ref() as *const JsString;
+        nodes.push(cons);
+    }
+    let text = nodes.last().unwrap().as_lossy_str();
+    assert_eq!(text.len(), 1 + 2000);
+    assert!(text.starts_with('x'));
+    assert!(text.ends_with('y'));
+}
+
+#[test]
+fn js_string_cons_empty_parts() {
+    // 双空串 Cons：空判定与长度均为 0，扁平化为空文本。
+    let left = Box::new(JsString::new(String::new()));
+    let right = Box::new(JsString::new(String::new()));
+    let cons = Box::new(unsafe { JsString::new_cons(&*left, &*right) });
+    assert!(cons.is_empty());
+    assert_eq!(cons.utf16_len(), 0);
+    assert_eq!(cons.as_lossy_str(), "");
+}
+
+#[test]
+fn new_empty_defaults() {
+    let obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert_eq!(obj.shape_id(), EMPTY_SHAPE_ID);
+    assert_eq!(obj.prop_count(), 0);
+    assert!(obj.is_extensible());
+    assert!(!obj.is_array());
+    assert!(!obj.is_function());
+    assert!(!obj.is_session_epoch());
+    assert_eq!(obj.generation(), 1);
+    assert!(obj.hash_props_vec().is_none());
+    assert!(!obj.has_prop_meta());
+}
+
+#[test]
+fn session_epoch_marker_roundtrip() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert!(!obj.is_session_epoch());
+    obj.set_session_epoch(true);
+    assert!(obj.is_session_epoch());
+    obj.set_session_epoch(false);
+    assert!(!obj.is_session_epoch());
+}
+
+#[test]
+fn session_epoch_marker_preserves_gc_mark_bit() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert!(!obj.is_gc_marked());
+    obj.set_gc_mark(true);
+    assert!(obj.is_gc_marked());
+    assert!(!obj.is_session_epoch());
+
+    obj.set_session_epoch(true);
+    assert!(obj.is_session_epoch());
+    assert!(obj.is_gc_marked());
+
+    obj.set_gc_mark(false);
+    assert!(!obj.is_gc_marked());
+}
+
+#[test]
+fn session_epoch_marker_keeps_object_size_bound() {
+    let sz = std::mem::size_of::<JsObject>();
+    assert!(sz <= 256, "JsObject grew unexpectedly: {sz}B");
+}
+
+#[test]
+fn clone_for_session_epoch_marks_clone_and_does_not_alias_hash_props() {
+    let mut source = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    source.set_prop_at(0, JsValue::int(1));
+
+    let mut clone = source.clone_for_session_epoch();
+    assert!(clone.is_session_epoch());
+    clone.set_prop_at(0, JsValue::int(2));
+
+    assert_eq!(source.get_prop_at(0), JsValue::int(1));
+    assert_eq!(clone.get_prop_at(0), JsValue::int(2));
+}
+
+#[test]
+fn clone_for_session_epoch_does_not_alias_prop_meta() {
+    let mut source = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    source.set_prop_at(0, JsValue::undefined());
+    source.set_accessor_meta(0, JsValue::int(10), JsValue::int(11), PropAttributes::DEFAULT_DATA);
+
+    let mut clone = source.clone_for_session_epoch();
+    clone.set_accessor_meta(0, JsValue::int(20), JsValue::int(21), PropAttributes::DEFAULT_DATA);
+
+    let source_meta = source.prop_meta_at(0).expect("source meta");
+    let clone_meta = clone.prop_meta_at(0).expect("clone meta");
+    assert_eq!(source_meta.get, JsValue::int(10));
+    assert_eq!(source_meta.set, JsValue::int(11));
+    assert_eq!(clone_meta.get, JsValue::int(20));
+    assert_eq!(clone_meta.set, JsValue::int(21));
+}
+
+#[test]
+fn shape_id_roundtrip() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    obj.set_shape_id(0x00AB_CDEF);
+    assert_eq!(obj.shape_id(), 0x00AB_CDEF);
+}
+
+#[test]
+fn prop_count_roundtrip() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert_eq!(obj.prop_count(), 0);
+    obj.ensure_hash_props().push(JsValue::int(17));
+    assert_eq!(obj.prop_count(), 1);
+}
+
+#[test]
+fn flags_individual() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert!(obj.is_extensible());
+    obj.set_extensible(false);
+    assert!(!obj.is_extensible());
+}
+
+#[test]
+fn hash_prop_read_write() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    obj.set_prop_at(0, JsValue::int(42));
+    assert_eq!(obj.get_prop_at(0), JsValue::int(42));
+}
+
+#[test]
+fn new_array_flags() {
+    let bump = bumpalo::Bump::new();
+    let obj = JsObject::new_array(5, JsValue::null(), 3, &bump);
+    assert!(obj.is_array());
+    assert_eq!(obj.shape_id(), 5);
+    assert_eq!(obj.prop_count(), 3);
+}
+
+#[test]
+fn generation_bump() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert_eq!(obj.generation(), 1);
+    obj.bump_generation();
+    assert_eq!(obj.generation(), 2);
+}
+
+#[test]
+fn hash_props_lazy_init() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    assert!(obj.hash_props_vec().is_none());
+    assert_eq!(obj.prop_count(), 0);
+    obj.set_prop_at(0, JsValue::int(1));
+    assert!(obj.hash_props_vec().is_some());
+    assert_eq!(obj.prop_count(), 1);
+}
+
+#[test]
+fn hash_props_flat_storage_roundtrip() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    obj.set_prop_at(0, JsValue::int(100));
+    obj.set_prop_at(1, JsValue::int(200));
+    assert_eq!(obj.get_prop_at(0), JsValue::int(100));
+    assert_eq!(obj.get_prop_at(1), JsValue::int(200));
+}
+
+#[test]
+fn prop_meta_lazy_init() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    obj.set_prop_at(0, JsValue::int(1));
+    assert!(!obj.has_prop_meta());
+
+    obj.set_data_meta(0, PropAttributes::new(false, true, false));
+    assert!(obj.has_prop_meta());
+    let meta = obj.prop_meta_at(0).expect("meta");
+    assert!(!meta.is_accessor);
+    assert!(!meta.attributes.writable());
+    assert!(meta.attributes.enumerable());
+    assert!(!meta.attributes.configurable());
+}
+
+#[test]
+fn accessor_meta_roundtrip_and_alignment() {
+    let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::null());
+    obj.set_prop_at(0, JsValue::int(1));
+    obj.set_accessor_meta(2, JsValue::int(10), JsValue::int(11), PropAttributes::new(false, false, true));
+
+    assert_eq!(obj.prop_count(), 3);
+    assert!(obj.is_accessor_meta(2));
+    let meta = obj.prop_meta_at(2).expect("accessor meta");
+    assert_eq!(meta.get, JsValue::int(10));
+    assert_eq!(meta.set, JsValue::int(11));
+    assert!(!meta.attributes.writable());
+    assert!(!meta.attributes.enumerable());
+    assert!(meta.attributes.configurable());
+
+    obj.push_prop(JsValue::int(4));
+    assert_eq!(obj.prop_meta_vec().expect("meta").len(), obj.prop_vec_len());
+}
+
+#[test]
+fn array_element_write_preserves_props_after_element_growth() {
+    // 先写属性再 push 元素：元素区增长必须整体搬移属性区，不覆盖属性。
+    let bump = bumpalo::Bump::new();
+    let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 3, &bump);
+    obj.set_prop_shape(0, JsValue::int(99));
+    obj.set_prop_at(3, JsValue::int(4));
+    assert_eq!(obj.prop_count(), 4);
+    assert_eq!(obj.get_prop_at(3), JsValue::int(4));
+    assert_eq!(obj.get_prop_shape(0), JsValue::int(99));
+}
+
+#[test]
+fn array_element_write_beyond_count_relocates_prop_zone() {
+    // 稀疏写入（越界索引）把属性区推到新元素之后，属性读取仍命中。
+    let bump = bumpalo::Bump::new();
+    let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 2, &bump);
+    obj.set_prop_shape(0, JsValue::int(7));
+    obj.set_prop_at(5, JsValue::int(50));
+    assert_eq!(obj.prop_count(), 6);
+    assert_eq!(obj.get_prop_at(5), JsValue::int(50));
+    assert_eq!(obj.get_prop_shape(0), JsValue::int(7));
+}
+
+#[test]
+fn array_prop_count_truncate_keeps_prop_zone() {
+    // pop 截断元素区时属性区不得被删（meta 同步 insert/drain 对齐）。
+    let bump = bumpalo::Bump::new();
+    let mut obj = JsObject::new_array(EMPTY_SHAPE_ID, JsValue::null(), 3, &bump);
+    obj.set_prop_shape(0, JsValue::int(5));
+    obj.set_data_meta(3, PropAttributes::new(true, false, true));
+    obj.set_prop_count_fast(2);
+    assert_eq!(obj.prop_count(), 2);
+    assert_eq!(obj.get_prop_shape(0), JsValue::int(5));
+    assert!(obj.prop_meta_at(2).is_some());
+}