I am using bitcore explorer and I want to initialize insight api in testnet. It has the following code. I try var insight = new Insight('testnet') but it is not working. What value for url should i input so that Networks.get(url) === testnet

function Insight(url, network) {
  if (!url && !network) {
    return new Insight(Networks.defaultNetwork);
  }
  if (Networks.get(url)) {
    network = Networks.get(url);
    if (network === Networks.livenet) {
      url = 'https://insight.bitpay.com';
    } else {
      url = 'https://test-insight.bitpay.com';
    }
  }
  JSUtil.defineImmutable(this, {
    url: url,
    network: Networks.get(network) || Networks.defaultNetwork
  });
  this.request = request;
  return this;
}