geotiff: add attrs canonical-tier locking test (#1984)

PR 4 of 7 from the attrs-contract plan in #1984. Adds
test_attrs_contract_canonical_1984.py: a single fixture that exercises
every canonical attr (crs, crs_wkt, transform, nodata, raster_type,
extra_tags, gdal_metadata, gdal_metadata_xml, x_resolution / y_resolution /
resolution_unit, _xrspatial_geotiff_contract), round-trips it through
to_geotiff -> open_geotiff, and asserts presence + value per key.

Sibling locking tests already cover the other tiers: aliases (#2002),
pass-through (#2004), and per-backend stamping of the contract version
(#2003). The canonical assertion list is what #1985 (parity matrix) and
#1986 (round-trip invariants) will import.

No production-code changes.

Author: brendancol

xrspatial/geotiff/tests/test_attrs_contract_canonical_1984.py

@@ -0,0 +1,294 @@
+"""Locking test for the canonical tier of the attrs contract.
+
+Issue #1984, PR 4 of 7.
+
+The attrs contract (see ``xrspatial/geotiff/_attrs.py`` and
+``docs/source/user_guide/attrs_contract.rst``) splits every key the
+read paths emit into three tiers. This file pins the *canonical* tier:
+keys xrspatial owns and guarantees round-trip stable through
+``to_geotiff`` -> ``open_geotiff``.
+
+Sibling files cover the other tiers:
+
+* ``test_attrs_contract_aliases_1984.py`` -- compatibility aliases.
+* ``test_attrs_contract_passthrough_1984.py`` -- best-effort
+  pass-through.
+* ``test_attrs_contract_version_1984.py`` -- per-backend stamping of
+  ``attrs['_xrspatial_geotiff_contract']`` (also canonical, kept in its
+  own file because the assertion is per read path rather than
+  per round-trip).
+
+The canonical keys locked here:
+
+* ``crs``                          -- EPSG integer code.
+* ``crs_wkt``                      -- horizontal CRS WKT string.
+* ``transform``                    -- rasterio-style 6-tuple.
+* ``nodata``                       -- declared file sentinel (GDAL_NODATA).
+* ``raster_type``                  -- 'point' (set explicitly) or absent
+                                      (= 'area', the implicit default).
+* ``extra_tags``                   -- list of (id, type, count, value)
+                                      tuples for out-of-band TIFF tags.
+* ``gdal_metadata``                -- dict parsed from GDAL_METADATA XML.
+* ``gdal_metadata_xml``            -- raw GDAL_METADATA XML string.
+* ``x_resolution``, ``y_resolution``,
+  ``resolution_unit``              -- TIFF XResolution / YResolution /
+                                      ResolutionUnit.
+* ``_xrspatial_geotiff_contract``  -- integer contract version. Stamped
+                                      on every read.
+
+The fixture below sets every canonical key on a synthetic DataArray,
+round-trips it through ``to_geotiff`` -> ``open_geotiff``, and the test
+suite below asserts both presence and value equality per key. The
+single-fixture shape is intentional: a future writer change that drops
+one canonical key shows up here as one failing assertion rather than
+being lost in a larger diff.
+
+Issues #1985 (parity matrix) and #1986 (round-trip invariants) consume
+this assertion list. If you add a key here, update the canonical block
+in the contract page and the ``_attrs.py`` module docstring as well.
+"""
+from __future__ import annotations
+
+import numpy as np
+import pytest
+import xarray as xr
+
+from xrspatial.geotiff import open_geotiff, to_geotiff
+from xrspatial.geotiff._attrs import _ATTRS_CONTRACT_VERSION
+
+
+_CONTRACT_KEY = '_xrspatial_geotiff_contract'
+
+# Every key the canonical tier guarantees round-trip stable. Keep the
+# order consistent with the contract docs so a diff here lines up with
+# a diff in ``attrs_contract.rst``.
+_CANONICAL_KEYS = (
+    'crs',
+    'crs_wkt',
+    'transform',
+    'nodata',
+    'extra_tags',
+    'gdal_metadata',
+    'gdal_metadata_xml',
+    'x_resolution',
+    'y_resolution',
+    'resolution_unit',
+    _CONTRACT_KEY,
+)
+
+# Fixture values, written into ``attrs`` on the synthetic DataArray and
+# compared to the read-back attrs after round-trip. ``transform`` is
+# pinned by ``y`` / ``x`` coords so we expect that exact 6-tuple back.
+_NODATA_SENTINEL = -9999.0
+_X_RES = 300.0
+_Y_RES = 300.0
+_RES_UNIT = 'inch'
+_GDAL_META = {'AREA_OR_POINT': 'Area', 'TIFFTAG_SOFTWARE': 'xrspatial-1984'}
+# Software tag (305, ASCII). Picked because it is benign (no spatial
+# interpretation, no security filter) and tifffile decodes it as-is.
+# Count must include the trailing NUL byte.
+_SOFTWARE_STR = 'xrspatial-canonical-1984'
+_EXTRA_TAGS = [(305, 2, len(_SOFTWARE_STR) + 1, _SOFTWARE_STR)]
+# ``crs_wkt`` is round-tripped via attrs['crs'] (the EPSG code drives
+# the writer), so we leave it for the reader to emit. Setting it on
+# write is allowed but not required; the read-back value comes from the
+# PROJ database.
+
+
+def _make_canonical_da():
+    """Build a synthetic DataArray exercising every canonical attr.
+
+    Returns the DataArray plus the expected ``transform`` tuple so the
+    test can assert on the round-tripped value without recomputing it.
+    """
+    h, w = 4, 4
+    data = np.arange(h * w, dtype=np.float32).reshape(h, w)
+    # Pin a non-identity transform so the round-trip check catches a
+    # writer that drops the tiepoint / pixel-scale tags. Coords are
+    # interpreted as pixel centres; the emitted transform's origin is
+    # the top-left corner, so origin_x = 100 - 10/2 = 95 and
+    # origin_y = 240 - (-10)/2 = 245.
+    x = np.array([100.0, 110.0, 120.0, 130.0], dtype=np.float64)
+    y = np.array([240.0, 230.0, 220.0, 210.0], dtype=np.float64)
+    expected_transform = (10.0, 0.0, 95.0, 0.0, -10.0, 245.0)
+
+    da = xr.DataArray(
+        data, dims=('y', 'x'), coords={'y': y, 'x': x},
+        attrs={
+            'crs': 4326,
+            'nodata': _NODATA_SENTINEL,
+            'extra_tags': list(_EXTRA_TAGS),
+            'gdal_metadata': dict(_GDAL_META),
+            'x_resolution': _X_RES,
+            'y_resolution': _Y_RES,
+            'resolution_unit': _RES_UNIT,
+        },
+    )
+    return da, expected_transform
+
+
+@pytest.fixture
+def canonical_roundtrip(tmp_path):
+    """Round-trip the canonical fixture through write -> read.
+
+    Returns ``(read_da, expected_transform)``. Scoped to one round-trip
+    per test so per-key assertions stay independent and a single failure
+    points at one key rather than cascading.
+    """
+    da, expected_transform = _make_canonical_da()
+    path = str(tmp_path / 'attrs_contract_canonical.tif')
+    to_geotiff(da, path)
+    rd = open_geotiff(path)
+    return rd, expected_transform
+
+
+# ---------------------------------------------------------------------------
+# Single-fixture coverage: every canonical key is present on read-back.
+# ---------------------------------------------------------------------------
+
+
+def test_every_canonical_key_present(canonical_roundtrip):
+    """Pin the canonical key set after a round-trip.
+
+    A writer that drops one canonical key (e.g. forgets to emit
+    GDAL_METADATA) shows up here as one missing key rather than as a
+    later equality failure with a less obvious cause.
+    """
+    rd, _ = canonical_roundtrip
+    missing = sorted(k for k in _CANONICAL_KEYS if k not in rd.attrs)
+    assert missing == [], (
+        f"canonical attrs missing after round-trip: {missing}. "
+        f"attrs keys present: {sorted(rd.attrs.keys())}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Per-key value assertions: each canonical key round-trips by value.
+# ---------------------------------------------------------------------------
+
+
+def test_crs_roundtrip(canonical_roundtrip):
+    rd, _ = canonical_roundtrip
+    assert rd.attrs['crs'] == 4326
+
+
+def test_crs_wkt_roundtrip(canonical_roundtrip):
+    """``crs_wkt`` is reader-emitted from the EPSG code. Pin presence
+    and the substring guarantee callers rely on -- the exact WKT string
+    is PROJ-version dependent, but ``WGS 84`` always appears."""
+    rd, _ = canonical_roundtrip
+    wkt = rd.attrs['crs_wkt']
+    assert isinstance(wkt, str) and len(wkt) > 0
+    assert 'WGS 84' in wkt, (
+        f"crs_wkt round-trip lost the CRS identity: {wkt!r}"
+    )
+
+
+def test_transform_roundtrip(canonical_roundtrip):
+    rd, expected_transform = canonical_roundtrip
+    t = tuple(rd.attrs['transform'])
+    assert t == pytest.approx(expected_transform), (
+        f"transform round-trip mismatch.\n  expected: {expected_transform}\n"
+        f"  got     : {t}"
+    )
+
+
+def test_nodata_roundtrip(canonical_roundtrip):
+    rd, _ = canonical_roundtrip
+    assert rd.attrs['nodata'] == _NODATA_SENTINEL
+
+
+def test_extra_tags_roundtrip(canonical_roundtrip):
+    """A non-friendly extra_tags entry (Software, 305) round-trips
+    intact. The writer must preserve unknown tags so users can attach
+    arbitrary metadata."""
+    rd, _ = canonical_roundtrip
+    got = rd.attrs['extra_tags']
+    # Look up tag 305 specifically; ordering and any reader-added
+    # entries are not part of the contract for this assertion.
+    by_id = {t[0]: t for t in got}
+    assert 305 in by_id, (
+        f"Software tag (305) missing from read-back extra_tags: {got}"
+    )
+    tag_id, type_id, count, value = by_id[305]
+    assert tag_id == 305
+    assert type_id == 2  # TIFF ASCII
+    assert value == _SOFTWARE_STR
+
+
+def test_gdal_metadata_roundtrip(canonical_roundtrip):
+    """The parsed dict survives the round-trip key-by-key. Allow extra
+    entries the reader might inject (e.g. ``STATISTICS_*``) so this
+    test is not a tripwire for unrelated reader changes."""
+    rd, _ = canonical_roundtrip
+    got = rd.attrs['gdal_metadata']
+    assert isinstance(got, dict), f"gdal_metadata is not a dict: {got!r}"
+    for k, v in _GDAL_META.items():
+        assert got.get(k) == v, (
+            f"gdal_metadata[{k!r}] mismatch.\n  expected: {v!r}\n"
+            f"  got     : {got.get(k)!r}\n  full read-back: {got!r}"
+        )
+
+
+def test_gdal_metadata_xml_roundtrip(canonical_roundtrip):
+    """The raw XML string is reconstructed by the writer from the
+    ``gdal_metadata`` dict. Pin presence + the substring that proves
+    our fixture survived; the exact XML formatting is writer-dependent."""
+    rd, _ = canonical_roundtrip
+    xml = rd.attrs['gdal_metadata_xml']
+    assert isinstance(xml, str) and xml.startswith('<GDALMetadata>')
+    assert 'xrspatial-1984' in xml, (
+        f"gdal_metadata_xml lost the fixture marker: {xml!r}"
+    )
+
+
+def test_resolution_group_roundtrip(canonical_roundtrip):
+    """``x_resolution`` / ``y_resolution`` / ``resolution_unit`` are
+    written and read as one logical unit -- pin them together so a
+    writer that drops one but keeps the others fails here."""
+    rd, _ = canonical_roundtrip
+    assert rd.attrs['x_resolution'] == pytest.approx(_X_RES)
+    assert rd.attrs['y_resolution'] == pytest.approx(_Y_RES)
+    assert rd.attrs['resolution_unit'] == _RES_UNIT
+
+
+def test_contract_version_roundtrip(canonical_roundtrip):
+    """``_xrspatial_geotiff_contract`` is stamped on every read; pin
+    that the canonical fixture sees the current version. Per-backend
+    coverage lives in ``test_attrs_contract_version_1984.py``."""
+    rd, _ = canonical_roundtrip
+    assert rd.attrs[_CONTRACT_KEY] == _ATTRS_CONTRACT_VERSION
+
+
+# ---------------------------------------------------------------------------
+# ``raster_type`` lives outside the shared fixture because the canonical
+# default ('area') is encoded as *absence* in attrs. The two branches need
+# different fixtures.
+# ---------------------------------------------------------------------------
+
+
+def test_raster_type_area_omitted_on_roundtrip(tmp_path):
+    """RasterPixelIsArea is the implicit default and is encoded as
+    *absence* of ``attrs['raster_type']``. A DataArray with no
+    ``raster_type`` attr must round-trip to a DataArray that still has
+    no ``raster_type`` attr."""
+    da, _ = _make_canonical_da()
+    assert 'raster_type' not in da.attrs
+    path = str(tmp_path / 'raster_type_area.tif')
+    to_geotiff(da, path)
+    rd = open_geotiff(path)
+    assert 'raster_type' not in rd.attrs, (
+        f"area is the implicit default but the reader emitted "
+        f"raster_type={rd.attrs['raster_type']!r}"
+    )
+
+
+def test_raster_type_point_roundtrip(tmp_path):
+    """``raster_type='point'`` is the only value the writer accepts via
+    attrs; the reader emits it back on a round-trip."""
+    da, _ = _make_canonical_da()
+    da.attrs['raster_type'] = 'point'
+    path = str(tmp_path / 'raster_type_point.tif')
+    to_geotiff(da, path)
+    rd = open_geotiff(path)
+    assert rd.attrs.get('raster_type') == 'point'