test(layoutConstants): add accessibility tests (#4639)

lib/svg/layoutConstants.accessibility.test.ts

@@ -0,0 +1,63 @@
+// lib/svg/layoutConstants.accessibility.test.ts
+
+import { describe, expect, it } from 'vitest';
+import {
+  GHOST_HEIGHT_PX,
+  LOG_SCALE_MULTIPLIER,
+  LINEAR_SCALE_MULTIPLIER,
+  MAX_LOG_HEIGHT,
+  MAX_LINEAR_HEIGHT,
+  TILE_WIDTH_HALF,
+  TILE_HEIGHT_HALF,
+  GRID_ORIGIN_X,
+  GRID_ORIGIN_Y,
+} from './layoutConstants';
+
+describe('Layout Constants Accessibility', () => {
+  it('provides positive height values so towers render visibly for screen-reader users', () => {
+    const heights = [GHOST_HEIGHT_PX, MAX_LOG_HEIGHT, MAX_LINEAR_HEIGHT];
+
+    heights.forEach((value) => {
+      expect(typeof value).toBe('number');
+      expect(value).toBeGreaterThan(0);
+      expect(Number.isFinite(value)).toBe(true);
+    });
+  });
+
+  it('caps tower heights below the SVG viewport so content never clips out of assistive-tech reach', () => {
+    // SVG canvas is 600x420 in this project; a safe upper bound for tower height
+    // is well under half the viewport so labels and stats remain visible.
+    const SAFE_MAX_HEIGHT = 200;
+
+    expect(MAX_LOG_HEIGHT).toBeLessThan(SAFE_MAX_HEIGHT);
+    expect(MAX_LINEAR_HEIGHT).toBeLessThan(SAFE_MAX_HEIGHT);
+    expect(GHOST_HEIGHT_PX).toBeLessThan(MAX_LINEAR_HEIGHT);
+  });
+
+  it('exposes positive scale multipliers so contribution data maps to a predictable visual hierarchy', () => {
+    expect(LOG_SCALE_MULTIPLIER).toBeGreaterThan(0);
+    expect(LINEAR_SCALE_MULTIPLIER).toBeGreaterThan(0);
+
+    // Logarithmic scaling must grow faster than linear at small values
+    // so low-activity users still get a visually meaningful tower.
+    expect(LOG_SCALE_MULTIPLIER).toBeGreaterThan(LINEAR_SCALE_MULTIPLIER);
+  });
+
+  it('anchors the grid origin inside the SVG canvas so the rendered city is reachable by visual focus order', () => {
+    // The SVG canvas spans 0..600 horizontally and 0..420 vertically.
+    expect(GRID_ORIGIN_X).toBeGreaterThan(0);
+    expect(GRID_ORIGIN_X).toBeLessThan(600);
+
+    expect(GRID_ORIGIN_Y).toBeGreaterThan(0);
+    expect(GRID_ORIGIN_Y).toBeLessThan(420);
+  });
+
+  it('keeps isometric tile halves positive so tower geometry stays parseable for screen-reader title tags', () => {
+    expect(TILE_WIDTH_HALF).toBeGreaterThan(0);
+    expect(TILE_HEIGHT_HALF).toBeGreaterThan(0);
+
+    // The isometric projection requires width-half > height-half to maintain
+    // the 2:1 aspect ratio used by every <title>-tagged tower group.
+    expect(TILE_WIDTH_HALF).toBeGreaterThan(TILE_HEIGHT_HALF);
+  });
+});