Add snapshot tests for CircularDependency formatting (#332)

[leynos]

Summary

Closes #332

Adds insta snapshot coverage for the user-facing IrGenError::CircularDependency message, following the established diagnostic_json_tests pattern (localiser lock + set_en_localizer + assert_snapshot!).

• circular_dependency_display — snapshots the Display rendering (Circular dependency detected: ["a", "b", "a"].).
• circular_dependency_error_json — snapshots the JSON diagnostic document via render_error_json (the plain-error path; IrGenError does not implement miette::Diagnostic, so render_diagnostic_json does not apply).

The error is produced through the real pipeline (manifest::from_str → BuildGraph::from_manifest) with a two-target cycle; the detector's canonical rotation keeps the snapshot deterministic.

Validation

• make check-fmt / make lint / make test — pass (37 suites; both snapshots committed and green)

🤖 Generated with Claude Code

Summary by Sourcery

Add snapshot-based regression tests for the CircularDependency IR generation error formatting.

Tests:

• Add snapshot test for the Display output of IrGenError::CircularDependency built via the real IR pipeline.
• Add snapshot test for the JSON error document produced for IrGenError::CircularDependency using render_error_json().

[coderabbitai]

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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[sourcery-ai]

Reviewer's Guide

Adds snapshot-based regression tests for the user-facing IrGenError::CircularDependency formatting (Display and JSON), using the existing diagnostic_json_tests insta test harness and a deterministic circular manifest built through the real IR pipeline.

File-Level Changes

Change	Details	Files
Add insta snapshot tests for IrGenError::CircularDependency Display and JSON output using the diagnostic_json_tests harness and a deterministic circular manifest.	Introduce helper function that constructs a manifest with two mutually dependent targets and builds the IR to yield a real IrGenError::CircularDependency via BuildGraph::from_manifest Add rstest-based snapshot test that locks localization, forces English localizer, and snapshots the error Display string using assert_snapshot! and snapshot_settings Add rstest-based snapshot test that renders the error to JSON via render_error_json, normalizes it through parse_json_value and serde_json::to_string_pretty, and snapshots the pretty JSON output Commit two new insta snapshot files under src/snapshots/diagnostic_json for the Display string and JSON diagnostic outputs respectively	src/diagnostic_json_tests.rs src/snapshots/diagnostic_json/netsuke__diagnostic_json__tests__circular_dependency_display.snap src/snapshots/diagnostic_json/netsuke__diagnostic_json__tests__circular_dependency_error_json.snap

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#332	Add insta snapshot tests in diagnostic_json_tests.rs for the formatted Display output of IrGenError::CircularDependency, following the existing localiser lock + set_en_localizer + assert_snapshot! pattern.	✅
#332	Add insta snapshot tests in diagnostic_json_tests.rs for the JSON diagnostic output of IrGenError::CircularDependency (via the error JSON renderer), following the existing snapshot pattern and using a representative cyclic manifest.	✅

Possibly linked issues

• Add insta snapshot tests for CircularDependency error message formatting #332: PR adds insta snapshot tests for IrGenError::CircularDependency Display and JSON, exactly as requested in the issue.

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