text: 
  const assert = require('assert');
  const Complex = require('../index');
  
  
  describe('test to cos method', () => {
      it('should the calculate the cos of a complex number', () => {
          const complex = new Complex(Math.PI, 0);
  
          const cosComplex = complex.cos();
          assert(cosComplex.real === -1);
          assert(cosComplex.imaginary < 0.0001);
      });
  
      it('should the calculate the cos of a complex number', () => {
          const cosComplex = Complex.cos({ r:Math.PI, i:0 });
          assert(cosComplex.real === -1);
          assert(cosComplex.imaginary < 0.0001);
      });
  });
  