test(array): replace example-based tests with PBT

- Verify array input returns same reference
- Verify non-array non-nullish input wraps in single-element array
- Verify null/undefined returns empty array
- Verify result is always an array

Property-based tests cover all original cases and more edge cases.

Author: ryoppippi

src/utils/array.test.ts

@@ -1,16 +1,31 @@
+import { fc, test as fcTest } from '@fast-check/vitest';
 import { toArray } from './array';
 
-describe('toArray', () => {
-	it.each([
-		[undefined, []],
-		[null, []],
-		[false, [false]],
-		[0, [0]],
-		['', ['']],
-		[[], []],
-		['foo', ['foo']],
-		[['foo'], ['foo']],
-	])('%s => %s', (input, expected) => {
-		expect(toArray(input)).toEqual(expected);
+describe('toArray - Property-Based Tests', () => {
+	fcTest.prop([fc.array(fc.anything())], { numRuns: 100 })(
+		'array input returns the same array reference',
+		(arr) => {
+			expect(toArray(arr)).toBe(arr);
+		},
+	);
+
+	fcTest.prop([fc.anything().filter((x) => !Array.isArray(x) && x != null)], { numRuns: 100 })(
+		'non-array non-nullish input returns single-element array',
+		(value) => {
+			const result = toArray(value);
+			expect(result).toHaveLength(1);
+			expect(result[0]).toBe(value);
+		},
+	);
+
+	fcTest.prop([fc.constantFrom(null, undefined)], { numRuns: 10 })(
+		'null or undefined returns empty array',
+		(value) => {
+			expect(toArray(value)).toEqual([]);
+		},
+	);
+
+	fcTest.prop([fc.anything()], { numRuns: 100 })('result is always an array', (value) => {
+		expect(Array.isArray(toArray(value))).toBe(true);
 	});
 });