Fix remaining append bugs in test_api

versioned_hdf5/backend.py

@@ -1008,7 +1008,7 @@ def __init__(self, value: np.ndarray):
         self.value = value
 
     def __repr__(self):
-        return f"WriteOperation: {self.value}"
+        return f"AppendOperation: {self.value}"
 
     def apply(
         self,
@@ -1229,7 +1229,7 @@ def append_to_dataset(
         )
 
     # Get the slices from the previous version; they are reused here
-    last_virtual_slice = list(sorted(slices, key=lambda obj: obj.args[0]))[-1]
+    last_virtual_slice = list(sorted(slices, key=lambda obj: obj.args[0].start))[-1]
 
     # Split the data to append into a part which fits in the last
     # chunk of the raw data, and the part that doesn't
@@ -1558,7 +1558,7 @@ def partition(
         index = to_slice_tuple(obj)
         shape = tuple(dim.stop for dim in index.args)
 
-    if isinstance(chunks, int):
+    if isinstance(chunks, (int, np.integer)):
         chunks = (chunks,)
 
     yield from ChunkSize(chunks).as_subchunks(index, shape)