test: add test helpers and simplify metadata tests

Author: d-v-b

tests/conftest.py

@@ -58,6 +58,25 @@
     from zarr.core.dtype.wrapper import ZDType
 
 
+@dataclass
+class Expect[TIn, TOut]:
+    """A test case with explicit input, expected output, and a human-readable id."""
+
+    input: TIn
+    output: TOut
+    id: str
+
+
+@dataclass
+class ExpectFail[TIn]:
+    """A test case that should raise an exception."""
+
+    input: TIn
+    exception: type[Exception]
+    id: str
+    msg: str | None = None
+
+
 async def parse_store(
     store: Literal["local", "memory", "fsspec", "zip", "memory_get_latency"], path: str
 ) -> LocalStore | MemoryStore | FsspecStore | ZipStore | LatencyStore:

tests/test_metadata/conftest.py

@@ -0,0 +1,41 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+from zarr.codecs.bytes import BytesCodec
+
+if TYPE_CHECKING:
+    from zarr.core.metadata.v3 import ArrayMetadataJSON_V3
+
+
+def minimal_metadata_dict_v3(
+    extra_fields: dict[str, Any] | None = None, **overrides: Any
+) -> ArrayMetadataJSON_V3:
+    """Build a minimal valid V3 array metadata JSON dict.
+
+    The output matches the shape of ``ArrayV3Metadata.to_dict()`` — all
+    fields that ``to_dict`` always emits are included.
+
+    Parameters
+    ----------
+    extra_fields : dict, optional
+        Extra keys to inject into the dict (e.g. extension fields).
+    **overrides
+        Override any of the standard metadata fields.
+    """
+    d: ArrayMetadataJSON_V3 = {
+        "zarr_format": 3,
+        "node_type": "array",
+        "shape": (4, 4),
+        "data_type": "uint8",
+        "chunk_grid": {"name": "regular", "configuration": {"chunk_shape": (4, 4)}},
+        "chunk_key_encoding": {"name": "default", "configuration": {"separator": "/"}},
+        "fill_value": 0,
+        "codecs": (BytesCodec().to_dict(),),
+        "attributes": {},
+        "storage_transformers": (),
+    }
+    d.update(overrides)
+    if extra_fields is not None:
+        d.update(extra_fields)
+    return d