Deterministically cover the scan-time DependencyError branch

[d-chambers]

Description

dev's codecov/project check is failing at 99.98% (target 100%), which hard-fails every open PR (it already showed up on #846 and #851). The two uncovered lines are the except DependencyError warn-and-continue branch in the scan loop (dascore/io/core.py:1393-1394).

That branch was only exercised indirectly by test_legacy_file_scan_warns_and_skips, which scans the legacy DASVader JLD2 file — and whether that raises DependencyError depends on the installed HDF5 stack. An upstream dependency update (first visible on the #845 merge CI run) made the legacy file scan cleanly, so the branch silently lost coverage.

This adds a deterministic test using a name-gated _DependencyErrorFormatter, mirroring the existing _MissingOptionalFormatter pattern, so the branch stays covered regardless of the HDF5 stack. Test-only change.

Changelog

none

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes.
• documented the new feature with docstrings and/or appropriate doc page.
• included tests. See testing guidelines.
• added the "ready_for_review" tag once the PR is ready to be reviewed.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of dependency-related file errors during scanning.
  • Dependency errors now generate warnings without preventing other readable files from being processed.

• Tests

  • Added coverage to verify warning behavior and continued scanning when dependency issues are encountered.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 5648147c-92e5-4177-b4d9-1a0ee6875908

📥 Commits

Reviewing files that changed from the base of the PR and between a005012 and c7f53c4.

📒 Files selected for processing (1)

• tests/test_io/test_io_core.py

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📝 Walkthrough

Walkthrough

Changes

The test suite now simulates DependencyError during scanning. It verifies that the error emits a warning, skips the affected file, and allows other readable files to produce results.

Dependency error scan handling

Layer / File(s)	Summary
Dependency error simulation and scan assertions tests/test_io/test_io_core.py	Adds the DependencyError import, a test formatter that raises the error for .dep files, and coverage for warning, skip, and fallback scan behavior.

Suggested labels: CI

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the problem, solution, scope, and test coverage, and it completes the applicable checklist items.
Title check	✅ Passed	The title clearly and concisely identifies the deterministic test coverage added for the scan-time DependencyError branch.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cover-scan-dependency-error

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a005012) to head (c7f53c4).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@             Coverage Diff             @@
##              dev      #852      +/-   ##
===========================================
+ Coverage   99.98%   100.00%   +0.01%     
===========================================
  Files         164       164              
  Lines       18192     18192              
===========================================
+ Hits        18190     18192       +2     
+ Misses          2         0       -2     

Flag	Coverage Δ
network	48.30% <ø> (ø)
unittests	100.00% <ø> (+0.01%)	⬆️

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