Create a testnet key pair

transaction.js

let bitcoin = require("bitcoinjs-lib");

function getNewAddress(){
	  let NETWORK = bitcoin.networks.testnet; //main net bitcoin.networks.bitcoin
	  let wif = bitcoin.ECPair.makeRandom({network: NETWORK}).toWIF();
	  let keyPair = bitcoin.ECPair.fromWIF(wif, NETWORK);
	  
	  //p2pkh
	  let p2pkhAddr = keyPair.getAddress();
	  
	  //native witness
	  let pubKey = keyPair.getPublicKeyBuffer();
	  let scriptPubKey = bitcoin.script.witnessPubKeyHash.output.encode(bitcoin.crypto.hash160(pubKey));
	  let p2wpkhAddr = bitcoin.address.fromOutputScript(scriptPubKey, NETWORK);
	  
	  //p2sh witness
	  let pubKeyHash = bitcoin.crypto.hash160(pubKey);
	  let redeemScript = bitcoin.script.witnessPubKeyHash.output.encode(pubKeyHash);
	  let redeemScriptHex = redeemScript.toString('hex');
	  let redeemScriptHash = bitcoin.crypto.hash160(redeemScript);
	  let scriptPubKey2 = bitcoin.script.scriptHash.output.encode(redeemScriptHash);
	  let p2shp2wpkhAddr = bitcoin.address.fromOutputScript(scriptPubKey2, NETWORK);
	  
	  return {
		  pk: wif,
		  p2pkh: p2pkhAddr,
		  p2wpkh: p2wpkhAddr,
		  p2shp2wpkh: p2shp2wpkhAddr,
		  redeemScript: redeemScriptHex
	  }; 
}

let keypair = getNewAddress();
let testnetaddress = keypair.p2pkh;
let testnetprivatekey = keypair.pk;

console.log(testnetaddress,testnetprivatekey);