geotiff: GPU + dask+GPU coverage for predictor=3 + integer reject (#1933)

[brendancol]

Summary

Closes a Cat 1 HIGH backend-parity gap for issue #1933 (_validate_predictor_sample_format). The eager numpy and dask paths are covered by test_predictor3_int_dtype_1933.py; the cupy and dask+cupy paths had no targeted tests.

The validator is invoked at two GPU sites:

• _backends/gpu.py:443 -- tiled eager GPU read
• _backends/gpu.py:999 -- GDS chunked GPU read

A regression dropping either call would let malformed predictor=3 + integer SampleFormat tiled files decode silently to garbage bytes on GPU.

9 new tests, all passing on a CUDA host:

• read_geotiff_gpu on stripped + tiled malformed files
• open_geotiff(gpu=True) and open_geotiff(chunks=, gpu=True) dispatchers
• read_geotiff_gpu(chunks=) on stripped + tiled
• Legitimate predictor=3 + float32 tiled file still round-trips on GPU (eager + dask+GPU)
• Error-message parity between GPU and eager paths

Mutation against the tiled GPU validator at gpu.py:443 flipped the tiled-raises test red. Mutation against the GDS chunked validator at gpu.py:999 flipped the chunked-tiled + chunked-dispatcher tests red.

This is a deep-sweep test-coverage PR. No source files were modified.

Test plan

• pytest xrspatial/geotiff/tests/test_predictor3_int_dtype_gpu_1933.py (9 passed)
• pytest xrspatial/geotiff/tests/test_predictor3_int_dtype_1933.py xrspatial/geotiff/tests/test_predictor3_int_dtype_gpu_1933.py (19 passed)
• Mutation: drop _validate_predictor_sample_format at gpu.py:443 -> test_gpu_eager_tiled_raises fails
• Mutation: drop _validate_predictor_sample_format at gpu.py:999 -> test_read_geotiff_gpu_chunked_tiled_raises + test_open_geotiff_chunks_gpu_dispatcher_raises fail

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[brendancol]

PR Review: geotiff: GPU + dask+GPU coverage for predictor=3 + integer reject (#1933)

Blockers (must fix before merge)

• None

Suggestions (should fix, not blocking)

• test_read_geotiff_gpu_chunked_tiled_raises (test_predictor3_int_dtype_gpu_1933.py:213) accepts the rejection from either the GDS validator at gpu.py:999 or the CPU dask fallback. On a host without KvikIO the GDS validator at line 999 is never exercised, so the mutation-kill claim in the PR description only holds on KvikIO-enabled CI. Consider gating the test on kvikio availability (pytest.importorskip("kvikio")) or adding a sibling test that does so, otherwise the line-999 call site is not actually pinned by the suite in the general case.
• test_predictor3_float32_gpu_round_trip and test_predictor3_float32_dask_gpu_round_trip (lines 245, 258) use tifffile.imwrite for the legitimate-file case while the malformed cases use the in-tree _assemble_standard_layout. Building the valid file through the same in-tree writer would remove the tifffile/imagecodecs skip dependency and keep the round-trip contract honest against the writer the rest of the suite exercises.

Nits (optional improvements)

• _build_predictor3_uint32_stripped_tiff (line 70) duplicates the helper in test_predictor3_int_dtype_1933.py:42. A shared helper in tests/conftest.py would keep the two modules from drifting if the malformed-file shape needs to change.
• Module docstring (lines 11-18) hard-codes gpu.py:443 and gpu.py:999. These will rot when the file is edited. A symbolic reference (the function name) would survive line renumbering.
• test_gpu_error_message_matches_eager (line 285) uses == on the full message. If the eager site ever appends file path or band info, both messages will diverge and the test fails for a non-regression. A startswith or shared substring check is more robust.

What looks good

• Tiled vs stripped split is well motivated: the stripped path falls through to the CPU validator, so the tiled fixture is what actually exercises gpu.py:443.
• Both dispatchers (open_geotiff(gpu=True) and open_geotiff(chunks=, gpu=True)) are covered alongside the direct read_geotiff_gpu entrypoints.
• Tmp filenames are unique per test, no collisions.
• Skip guard via cupy.cuda.is_available() is correct and keeps the file inert on non-GPU CI.
• Test-only PR, no source changes, matches the deep-sweep coverage charter.

Checklist

• Algorithm matches reference/paper (validator behaviour, no algorithm change)
• All implemented backends produce consistent results (parity test asserts identical message)
• NaN handling is correct (n/a, integer rejection)
• Edge cases are covered by tests (tiled + stripped + dispatcher + chunked)
• Dask chunk boundaries handled correctly (chunked tests use chunks= smaller than the array)
• No premature materialization or unnecessary copies
• Benchmark exists or is not needed (not needed, error path)
• README feature matrix updated (if applicable) (n/a)
• Docstrings present and accurate (modulo the line-number rot nit)

[brendancol]

PR Review: geotiff: GPU + dask+GPU coverage for predictor=3 + integer reject (#1933) (re-review after rebase)

Rebased cleanly onto origin/main at 1e34c92, picking up the Windows fix from 9ce0e60. Local run of xrspatial/geotiff/tests/test_predictor3_int_dtype_gpu_1933.py passes (8 passed, 1 skipped on CPU-only host where libkvikio is unavailable).

Blockers

• None

Suggestions

• None

Nits

• The pytest.importorskip("kvikio") call raises a PytestDeprecationWarning on hosts where the kvikio module is importable but its shared library is missing. Passing exc_type=ImportError would silence the warning ahead of pytest 9.1, but this is cosmetic.

What looks good

• Test coverage now spans cupy and dask+cupy paths for the predictor=3 + integer SampleFormat reject behavior added in geotiff: predictor=3 + integer dtype silently misdecoded on read #1933.
• The in-tree writer keeps the round-trip tests self-contained and avoids relying on any external writer behavior.
• kvikio gating via importorskip keeps the GPU-only tests honest on CPU CI runners.

Checklist

• Rebase clean on origin/main
• Tests pass locally
• No code changes beyond rebase
• Pushed with --force-with-lease to fork

[brendancol]

Rebased onto current main at 4dec5b6 to pick up the Python 3.14 CI matrix limit (b1579f8).