correct array.nbytes, and add tests

Author: d-v-b

src/zarr/core/array.py

@@ -977,9 +977,10 @@ def _iter_chunk_regions(
     @property
     def nbytes(self) -> int:
         """
-        The number of bytes that can be stored in this array.
+        The number of bytes that can be stored in the chunks of this array.
         """
-        return self.nchunks * self.dtype.itemsize
+        # TODO: how can this be meaningful for variable-length types?
+        return int(np.prod(self.shape) * self.dtype.itemsize)
 
     async def _get_selection(
         self,

tests/test_array.py

@@ -776,3 +776,21 @@ async def test_special_complex_fill_values_roundtrip(fill_value: Any, expected:
     assert content is not None
     actual = json.loads(content.to_bytes())
     assert actual["fill_value"] == expected
+
+
+@pytest.mark.parametrize("shape", [(1,), (2, 3), (4, 5, 6)])
+@pytest.mark.parametrize("dtype", ["uint8", "float32"])
+@pytest.mark.parametrize("array_type", ["async", "sync"])
+async def test_nbytes(
+    shape: tuple[int, ...], dtype: str, array_type: Literal["async", "sync"]
+) -> None:
+    """
+    Test that the ``nbytes`` attribute of an Array or AsyncArray correctly reports the capacity of
+    the chunks of that array.
+    """
+    store = MemoryStore()
+    arr = Array.create(store=store, shape=shape, dtype=dtype, fill_value=0)
+    if array_type == "async":
+        assert arr._async_array.nbytes == np.prod(arr.shape) * arr.dtype.itemsize
+    else:
+        assert arr.nbytes == np.prod(arr.shape) * arr.dtype.itemsize