text: describe('Teste do toBeNull', () => {
      it('deve demonstrar o uso do toBeNull', () => {
          let n1 = null;
          let n2 = undefined;
          let n3;
          let n4 = NaN;
          let n5 = 'Teste';
  
          expect(n1).toBeNull();
          expect(n2).not.toBeNull();
          expect(n3).not.toBeNull();
          expect(n4).not.toBeNull();
          expect(n5).not.toBeNull();
      });
  });