Added test suite

tests/type.spec.ts

@@ -0,0 +1,18 @@
+import {Writable} from '../src';
+
+describe('Type Utilities', () => {
+	describe('Writable', () => {
+		it('should create a writable version of a readonly type', () => {
+			type ReadonlyPerson = {
+				readonly name: string;
+				readonly age: number;
+			};
+			type WritablePerson = Writable<ReadonlyPerson>;
+			// Typescript: WritablePerson's properties should not be readonly
+			const person: WritablePerson = { name: 'Alice', age: 40 };
+			person.name = 'Bob'; // Should not error in TypeScript
+			person.age = 41;     // Should not error in TypeScript
+			expect(person).toEqual({ name: 'Bob', age: 41 });
+		});
+	});
+});