test: add vitest and svelte testing library (resolves #13)

src/lib/extractFormData.test.ts

@@ -0,0 +1,46 @@
+import { describe, it, expect } from 'vitest';
+import { extractFormData } from './extractFormData';
+import * as v from 'valibot';
+
+describe('extractFormData', () => {
+	it('should successfully extract and validate correct form data', async () => {
+		const formData = new FormData();
+		formData.append('name', 'John Doe');
+		formData.append('age', '30');
+
+		const request = new Request('http://localhost', {
+			method: 'POST',
+			body: formData
+		});
+
+		const schema = v.object({
+			name: v.string(),
+			age: v.string()
+		});
+
+		const result = await extractFormData(request, schema);
+
+		expect(result.error).toBeNull();
+		expect(result.data).toEqual({ name: 'John Doe', age: '30' });
+	});
+
+	it('should fail validation with missing required fields', async () => {
+		const formData = new FormData();
+		formData.append('age', '30');
+
+		const request = new Request('http://localhost', {
+			method: 'POST',
+			body: formData
+		});
+
+		const schema = v.object({
+			name: v.string(),
+			age: v.string()
+		});
+
+		const result = await extractFormData(request, schema);
+
+		expect(result.data).toBeUndefined();
+		expect(result.error).toBeTypeOf('string');
+	});
+});