Add unit tests for shape_utility pure functions

[tarone-saloni]

What this does

Adds a #[cfg(test)] module to editor/src/messages/tool/common_functionality/shapes/shape_utility.rs, which previously had no test coverage. All tests are pure unit tests — no editor setup or async runtime needed.

Functions covered

wrap_to_tau(angle)

Normalises an angle in radians to [0, 2π). Tests verify:

• Zero stays zero
• Angle already in range passes through unchanged
• Exactly TAU wraps to zero
• Values beyond TAU reduce to the remainder
• Negative angles wrap correctly

format_rounded(value, precision)

Formats a float and trims trailing zeros and the decimal point. Tests verify:

• Trailing zeros and dot are stripped (1.000 → "1")
• Partial trailing zeros are stripped (1.50 → "1.5")
• Significant digits are preserved (1.23 → "1.23")
• Rounding up works (3.14159 with precision 3 → "3.142")
• Zero precision and zero value

calculate_display_angle(angle)

Converts an angle in degrees to a display-friendly value, normalising full turns. Tests cover all three branches (positive, negative, zero) and the wrap-at-±360° edge cases.

arc_end_points_ignore_layer(radius, start, sweep, viewport)

Calculates arc start/end points in local or viewport space. Tests cover:

• Zero sweep (both points coincide)
• Quarter-circle and half-circle sweeps (exact coordinate verification)
• Radius scaling
• Identity viewport produces identical results to None

star_vertex_position(viewport, index, n, r1, r2)

Computes a star vertex in viewport space. Tests verify:

• Even index → outer radius (r1)
• Odd index → inner radius (r2)
• Correct angle formula for each vertex

polygon_vertex_position(viewport, index, n, radius)

Computes a regular polygon vertex. Tests verify vertex 0 (top), vertex 1 (right), vertex 2 (bottom) for a square.

inside_polygon(viewport, n, radius, point) and inside_star(viewport, n, r1, r2, point)

Winding-number hit-tests. Tests cover:

• Centre is inside
• Far-away point fails the bounding-box early-exit
• Point just beyond the outermost vertex/tip is outside
• Point near centre is inside

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive suite of unit tests for shape utility functions, covering angle wrapping, coordinate calculations for arcs, stars, and polygons, and hit-testing logic. The feedback identifies opportunities to improve test maintainability and readability by implementing a custom macro for floating-point approximations and utilizing idiomatic vector comparison methods from the glam library.

[gemini-code-assist]

There are many floating-point comparisons in these tests using the pattern (a - b).abs() < 1e-10. To improve readability and provide better failure messages, consider defining a local assert_approx_eq! macro at the top of the tests module.

macro_rules! assert_approx_eq {
    ($a:expr, $b:expr, $eps:expr) => {
        assert!(
            ($a - $b).abs() < $eps,
            "assertion failed: `(left - right).abs() < epsilon`\n  left: `{:?}`\n right: `{:?}`\nepsilon: `{:?}`",
            $a, $b, $eps
        );
    };
    ($a:expr, $b:expr) => {
        assert_approx_eq!($a, $b, 1e-10);
    };
}

This would allow you to write this assertion as assert_approx_eq!(wrap_to_tau(PI), PI); and can be used for all scalar float comparisons in this test module, making them more concise and readable.

[gemini-code-assist]

These per-component assertions can be simplified by using glam::DVec2::abs_diff_eq for a more concise and idiomatic vector comparison.

For example, these four lines can be replaced with:

let expected = DVec2::new(1., 0.);
assert!(start.abs_diff_eq(expected, 1e-10), "start point mismatch");
assert!(end.abs_diff_eq(expected, 1e-10), "end point mismatch");

This approach can be applied to other vector comparisons in this file (e.g., in arc_endpoints_with_identity_viewport_matches_no_viewport, star_vertex_*, and polygon_vertex_* tests) to make them cleaner and more readable.