refactor: standardize error snapshot testing with expect_snapshot_igraph_error()

[Copilot]

Addresses review feedback from #2515 to improve consistency and stability of error message testing.

Changes

• Standardized error snapshots: Replaced 67 occurrences of expect_snapshot(error = TRUE) with expect_snapshot_igraph_error() across 24 test files. This ensures line numbers in error messages are normalized to xx for stability. Includes both single-line and multi-line patterns where error = TRUE appeared on a separate line.

• Isolated test function: Moved Rx_igraph_test_error_with_source() from rinterface_extra.c (line 7766) to dedicated file test_error_with_source.c (line 31). Prevents unrelated changes from invalidating error line number tests.

• Exception documented: Added comment in test-error-formatting.R explaining why it retains expect_snapshot(error = TRUE) - needs actual line numbers for validation.

Technical Notes

Updated sources-glue-c.mk to include new C file in build. Snapshot updated to reflect new source location.

Note: test-games.R retains 2 instances of expect_snapshot(error = TRUE) with custom transform functions that would conflict with the built-in transform in expect_snapshot_igraph_error().

Testing

• ✅ Full test suite run: 7,511 tests passed, 0 failed
• ✅ All snapshots are current and accepted

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[krlmlr]

@copilot: Good job. Also run the tests and accept snapshots when done.

[krlmlr]

Look harder for usages where error = TRUE is on a separate line.

[Copilot]

Fixed in 4a4a599. Found and transformed 10 additional occurrences where error = TRUE was on a separate line in: test-flow.R (4), test-conversion.R (2), test-foreign.R (2), test-make.R (1), test-minimum.spanning.tree.R (1), test-other.R (1), test-utils-assert-args.R (1). All tests pass.

[Copilot]

@copilot: Good job. Also run the tests and accept snapshots when done.

Completed in 4a4a599. Full test suite run: 7511 tests passed, 0 failed. All snapshots are current and accepted.

[Copilot]

Pull request overview

This PR standardizes error snapshot testing across the test suite by introducing a consistent helper function and isolating test infrastructure for better stability.

Changes:

• Replaced 67 occurrences of expect_snapshot(error = TRUE) with expect_snapshot_igraph_error() across 24 test files, ensuring line numbers in error messages are normalized to xx for stability
• Moved the test error function Rx_igraph_test_error_with_source() from rinterface_extra.c to a dedicated file test_error_with_source.c to prevent unrelated changes from invalidating error line number tests
• Added explanatory comment in test-error-formatting.R documenting why it retains expect_snapshot(error = TRUE) (needs actual line numbers for validation)

Reviewed changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/testthat/test-versions.R	Converted 8 error snapshot tests to use standardized helper
tests/testthat/test-utils-assert-args.R	Converted 1 multi-line error snapshot to single-line helper call
tests/testthat/test-structural-properties.R	Converted 2 deprecated argument tests to use standardized helper
tests/testthat/test-plot.R	Converted 1 layout error test to use standardized helper
tests/testthat/test-other.R	Converted 2 error snapshots to use standardized helper
tests/testthat/test-minimum.spanning.tree.R	Converted 1 algorithm error test to use standardized helper
tests/testthat/test-make.R	Converted 4 error snapshot tests to use standardized helper
tests/testthat/test-layout.R	Converted 3 layout error tests to use standardized helper
tests/testthat/test-iterators.R	Converted 2 logical index tests to use standardized helper
tests/testthat/test-interface.R	Converted 3 error tests to use standardized helper
tests/testthat/test-incidence.R	Converted 4 biadjacency matrix error tests to use standardized helper
tests/testthat/test-hrg.R	Converted 2 argument validation tests to use standardized helper
tests/testthat/test-foreign.R	Converted 5 file format error tests to use standardized helper
tests/testthat/test-flow.R	Converted 11 flow algorithm error tests to use standardized helper
tests/testthat/test-fit.R	Converted 1 power law fitting error test to use standardized helper
tests/testthat/test-error-formatting.R	Added explanatory comment for retaining expect_snapshot(error = TRUE)
tests/testthat/test-conversion.R	Converted 5 conversion error tests to use standardized helper
tests/testthat/test-centrality.R	Converted 1 arpack error test to use standardized helper
tests/testthat/test-attributes.R	Converted 9 attribute error tests to use standardized helper
tests/testthat/test-adjacency.R	Converted 1 adjacency matrix NA test to use standardized helper
tests/testthat/_snaps/error-formatting.md	Updated snapshot to reflect new source location (test_error_with_source.c:31)
src/test_error_with_source.c	New dedicated file containing isolated test error function
src/test_error_with_source.dd	Build dependency file for new test source file
src/sources-glue-c.mk	Updated build configuration to include new test source file
src/rinterface_extra.c	Removed test error function (moved to dedicated file)