mermaid-render: python: pytest suite with _RUST_AVAILABLE guard

[hartsock]

Phase: 5 • Branch: mermaid-render/5.4-py-pytest-suite

What

Write tests/test_python_bindings.py mirroring scrybe-mermaid pattern: skip individual tests when _RUST_AVAILABLE is False, otherwise run real round-trip tests.

Files

• scrybe-mermaid-render/tests/test_python_bindings.py

Tests

• 5+ pytest cases: import works, render_to_svg returns <svg, embedded <metadata> present, raises on bad input, png feature path is skipped when not built.

Acceptance

• pytest tests/test_python_bindings.py -v all PASS in a venv with maturin-develop'd wheel.

Refs

#37 gating checklist box "Phase 6" • swarm.toml phase-5 goal 0.

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