Add validation and test coverage for tensorstore_cache_bytes edge cases

[Copilot]

Addresses unresolved review comments from PR #59 regarding validation and test coverage for tensorstore_cache_bytes parameter edge cases.

Changes

• Added negative value validation: Raises ValueError when tensorstore_cache_bytes < 0, either from direct parameter or CELLMAP_TENSORSTORE_CACHE_BYTES environment variable

• Added test coverage for tensorstore_cache_bytes=0: Verifies that zero correctly disables TensorStore's in-memory cache (per TensorStore documentation, total_bytes_limit=0 disables the LRU cache)

• Added validation tests:

  • Negative parameter values rejected
  • Negative environment variable values rejected
  • Non-integer environment variable values rejected (already implemented, now tested)

Example Usage

# Disable caching entirely
loader = CellMapDataLoader(dataset, tensorstore_cache_bytes=0)

# Negative values now raise clear errors
loader = CellMapDataLoader(dataset, tensorstore_cache_bytes=-100)
# ValueError: tensorstore_cache_bytes must be >= 0 when set; got -100

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[Copilot]

Pull request overview

This PR addresses unresolved review comments from PR #59 by adding validation and test coverage for tensorstore_cache_bytes parameter edge cases in the CellMapDataLoader. The changes ensure that invalid values (negative numbers, non-integers from environment variables) are properly rejected with clear error messages, and that the special case of zero (which disables caching) is explicitly tested and documented.

Changes:

• Added validation to reject negative tensorstore_cache_bytes values from both direct parameters and the CELLMAP_TENSORSTORE_CACHE_BYTES environment variable
• Added test coverage for tensorstore_cache_bytes=0 to verify it correctly disables TensorStore's in-memory cache
• Added comprehensive validation tests for negative values and invalid environment variable inputs

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/cellmap_data/dataloader.py	Added negative value validation check (lines 173-176) and formatting improvements (blank lines)
tests/test_dataloader.py	Added 4 new test methods covering zero-byte cache behavior and validation of negative/invalid inputs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.38%. Comparing base (ea597bf) to head (eeeceb8).
⚠️ Report is 5 commits behind head on cache_bound.

Additional details and impacted files

@@               Coverage Diff               @@
##           cache_bound      #60      +/-   ##
===============================================
+ Coverage        70.28%   70.38%   +0.09%     
===============================================
  Files               28       28              
  Lines             2628     2630       +2     
===============================================
+ Hits              1847     1851       +4     
+ Misses             781      779       -2     

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