Strengthen pickling test and fix ZipStore __getstate__() (zarr-developers#2807)

* Strenghten serialization test

* Fix ZipStore serialization

* Add changelog bug fix

Author: maxrjones

changes/2807.bugfix.rst

@@ -0,0 +1 @@
+Fix pickling for ZipStore

src/zarr/storage/_zip.py

@@ -108,7 +108,8 @@ async def _open(self) -> None:
         self._sync_open()
 
     def __getstate__(self) -> dict[str, Any]:
-        state = self.__dict__
+        # We need a copy to not modify the state of the original store
+        state = self.__dict__.copy()
         for attr in ["_zf", "_lock"]:
             state.pop(attr, None)
         return state

src/zarr/testing/store.py

@@ -99,10 +99,16 @@ def test_store_eq(self, store: S, store_kwargs: dict[str, Any]) -> None:
         store2 = self.store_cls(**store_kwargs)
         assert store == store2
 
-    def test_serializable_store(self, store: S) -> None:
+    async def test_serializable_store(self, store: S) -> None:
         new_store: S = pickle.loads(pickle.dumps(store))
         assert new_store == store
         assert new_store.read_only == store.read_only
+        # quickly roundtrip data to a key to test that new store works
+        data_buf = self.buffer_cls.from_bytes(b"\x01\x02\x03\x04")
+        key = "foo"
+        await store.set(key, data_buf)
+        observed = await store.get(key, prototype=default_buffer_prototype())
+        assert_bytes_equal(observed, data_buf)
 
     def test_store_read_only(self, store: S) -> None:
         assert not store.read_only