text: // tests/circle.test.js
  const circle = require('../src/circle');
  
  test('Circle area', () => {
      expect(circle.area(5)).toBeCloseTo(78.54);
      expect(circle.area()).toBeNaN();
  });
  
  test('Circumference', () => {
      expect(circle.circumference(11)).toBeCloseTo(69.1, 1);
      expect(circle.circumference()).toBeNaN();
  });