message: Added test for isOpen function
diff: @@ -23,4 +23,12 @@ describe('Listener', () => {
  expect('ws://localhost:3000/ws').to.be.equal(listener.url);
  listener.close();
  });
  +
  + describe('isOpen', () => {
  + it('should return false when listener is created and not opened', () => {
  + const listener = new Listener('ws://localhost:3000');
  + expect(listener.isOpen()).to.be.false;
  + listener.close();
  + });
  + });
  });
  