Working on tests for generate chunk key function

virtualizarr/tests/test_writers/test_icechunk.py

@@ -12,7 +12,7 @@
 from zarr import Array, Group, group  # type: ignore[import-untyped]
 
 from virtualizarr.manifests import ChunkManifest, ManifestArray
-from virtualizarr.writers.icechunk import dataset_to_icechunk
+from virtualizarr.writers.icechunk import dataset_to_icechunk, generate_chunk_key
 from virtualizarr.zarr import ZArray
 
 if TYPE_CHECKING:
@@ -288,3 +288,45 @@ def test_write_loadable_variable(
 # TODO test writing to a group that isn't the root group
 
 # TODO test with S3 / minio
+
+
+def test_generate_chunk_key_no_offset():
+    # Test case without any offset (append_axis and existing_num_chunks are None)
+    index = (1, 2, 3)
+    result = generate_chunk_key(index)
+    assert result == "1/2/3", "The chunk key should match the index without any offset."
+
+
+def test_generate_chunk_key_with_offset():
+    # Test case with offset on append_axis 1
+    index = (1, 2, 3)
+    append_axis = 1
+    existing_num_chunks = 5
+    result = generate_chunk_key(
+        index, append_axis=append_axis, existing_num_chunks=existing_num_chunks
+    )
+    assert result == "1/7/3", "The chunk key should offset the second index by 5."
+
+
+def test_generate_chunk_key_zero_offset():
+    # Test case where existing_num_chunks is 0 (no offset should be applied)
+    index = (4, 5, 6)
+    append_axis = 1
+    existing_num_chunks = 0
+    result = generate_chunk_key(
+        index, append_axis=append_axis, existing_num_chunks=existing_num_chunks
+    )
+    assert (
+        result == "4/5/6"
+    ), "No offset should be applied when existing_num_chunks is 0."
+
+
+def test_generate_chunk_key_append_axis_out_of_bounds():
+    # Edge case where append_axis is out of bounds
+    index = (3, 4)
+    append_axis = 2  # This is out of bounds for a 2D index
+    with pytest.raises(IndexError):
+        generate_chunk_key(index, append_axis=append_axis, existing_num_chunks=1)
+
+
+# Run tests using pytest

virtualizarr/writers/icechunk.py

@@ -194,6 +194,19 @@ def write_virtual_variable_to_icechunk(
     )
 
 
+def generate_chunk_key(
+    index: np.nditer.multi_index,
+    append_axis: Optional[int] = None,
+    existing_num_chunks: Optional[int] = None,
+) -> str:
+    if append_axis is not None:
+        list_index = list(index)
+        # Offset by the number of existing chunks on the append axis
+        list_index[append_axis] += existing_num_chunks
+        index = tuple(list_index)
+    return "/".join(str(i) for i in index)
+
+
 def write_manifest_virtual_refs(
     store: "IcechunkStore",
     group: "Group",
@@ -209,6 +222,8 @@ def write_manifest_virtual_refs(
     # loop over every reference in the ChunkManifest for that array
     # TODO inefficient: this should be replaced with something that sets all (new) references for the array at once
     # but Icechunk need to expose a suitable API first
+    # Aimee: the manifest (and it's corresponding paths, offsets and lengths, already has the shape of the datacube's chunks
+    # so we want to increment the resulting multi index
     it = np.nditer(
         [manifest._paths, manifest._offsets, manifest._lengths],  # type: ignore[arg-type]
         flags=[
@@ -220,13 +235,9 @@ def write_manifest_virtual_refs(
     )
 
     for path, offset, length in it:
+        # it.multi_index will be an iterator of the chunk shape
         index = it.multi_index
-        if append_axis is not None:
-            list_index = list(index)
-            # Offset by the number of existing chunks on the append axis
-            list_index[append_axis] += existing_num_chunks
-            index = tuple(list_index)
-        chunk_key = "/".join(str(i) for i in index)
+        chunk_key = generate_chunk_key(index, append_axis, existing_num_chunks)
 
         # set each reference individually
         store.set_virtual_ref(