chore(world): add tests for getFade and getSizeCategory

src/spec/world.spec.ts

@@ -0,0 +1,36 @@
+import { getSizeCategory, getFade } from '../lib/world.js';
+import { describe, expect, test } from 'vitest';
+
+describe('world', () => {
+  describe('getFade', () => {
+    test('should return expected fade for distance of 1000.0 and size category of 0', () => {
+      expect(getFade(1000.0, 0)).toBe(0.0);
+    });
+
+    test('should return expected fade for distance of 1.0 and size category of 4', () => {
+      expect(getFade(1.0, 4)).toBe(1.0);
+    });
+
+    test('should return expected fade for distance of 145.0 and size category of 1', () => {
+      expect(getFade(145.0, 1)).toBe(0.5);
+    });
+
+    test('should return expected fade for distance of 149.999 and size category of 1', () => {
+      expect(getFade(149.999, 1)).toBe(0.0);
+    });
+
+    test('should return expected fade for distance of 140.001 and size category of 1', () => {
+      expect(getFade(140.001, 1)).toBe(1.0);
+    });
+  });
+
+  describe('getSizeCategory', () => {
+    test('should return expected category for size of 0.1', () => {
+      expect(getSizeCategory(0.1)).toBe(0);
+    });
+
+    test('should return expected category for size of 4.0', () => {
+      expect(getSizeCategory(4.0)).toBe(1);
+    });
+  });
+});