text: // native tests doesn't do any smart contract(s) interaction
  
  // using the BDD with chai in this test script
  
  // Zeppelin test helpers
  const {
  	BN,
  	balance,
  	constants,
  	expectEvent,
  	expectRevert,
  } = require("@openzeppelin/test-helpers");
  const {
  	assert,
  	expect,
  } = require("chai");
  // enable chai-bn plugin
  // require('chai').use(require('chai-bn')(web3.utils.BN));
  const {
  	ZERO_ADDRESS,
  	ZERO_BYTES32,
  	MAX_UINT256,
  } = constants;
  
  // BN utils
  const {
  	print_amt,
  } = require("../scripts/include/bn_utils");
  
  // block utils
  const {
  	extract_gas_cost,
  } = require("./include/block_utils");
  
  // Truffle style contract testing
  contract("Native Tests: no smart contract interaction", function(accounts) {
  	// native transfer cost: 21,000 gas
  	// default gas cost: 21 Gwei
  	const min_balance = new BN(21_000 * 21).mul(new BN(10).pow(new BN(9)));
  
  	it("some accounts exist", async function() {
  		expect(accounts, "accounts array is undefined").to.exist;
  		expect(accounts.length, "accounts array is empty").to.be.gt(0);
  	});
  	it("default account has some native currency", async function() {
  		expect(await balance.current(accounts[0])).to.be.bignumber.greaterThan("0");
  	});
  	it(`default account has more than ${min_balance} native currency`, async function() {
  		expect(await balance.current(accounts[0])).to.be.bignumber.greaterThan(min_balance);
  	});
  	it("at least 2 accounts exist", async function() {
  		expect(accounts.length, "accounts array is empty").to.be.gt(1);
  	});
  	for(let i = 0; i < accounts.length; i++) {
  		it(`account${i} balance can be fetched`, async function() {
  			const tracker = await balance.tracker(accounts[i]);
  			console.log(`account${i} %o balance: %o`, accounts[i], print_amt(await tracker.get()));
  		});
  	}
  	describe("native transfer succeeds", function() {
  		let tracker0, tracker1;
  		before(async function() {
  			tracker0 = await balance.tracker(accounts[0]);
  			tracker1 = await balance.tracker(accounts[1]);
  		});
  
  		let value, receipt;
  		before(async function() {
  			const balance0 = await tracker0.get();
  			value = BN.min(balance0.sub(min_balance), new BN(10).pow(new BN(15)));
  			console.log("sending %o from account0 to account1", print_amt(value));
  			receipt = await web3.eth.sendTransaction({
  				from: accounts[0],
  				to: accounts[1],
  				value,
  			});
  			console.log("%o: fee %o", receipt.transactionHash, print_amt(await extract_gas_cost(receipt)));
  		});
  /*
  		after(async function() {
  			const balance1 = await tracker1.get();
  			value = balance1.sub(min_balance);
  			console.log("sending %o from account1 to account0", print_amt(value));
  			receipt = await web3.eth.sendTransaction({
  				from: accounts[1],
  				to: accounts[0],
  				value,
  			});
  			console.log("%o: fee %o", receipt.transactionHash, print_amt(await extract_gas_cost(receipt)));
  		});
  */
  		it("transfer cost is 21,000 gas", async function() {
  			expect(receipt.gasUsed).to.be.equal(21_000);
  		});
  		it("account 0 balance decreases as expected", async function() {
  			const deltaWithFees = await tracker0.deltaWithFees();
  			const delta = deltaWithFees.delta;
  			const fees = deltaWithFees.fees;
  			expect(delta).to.be.bignumber.that.equals(value.neg().sub(fees));
  		});
  		it("account 1 balance increases as expected", async function() {
  			expect(await tracker1.delta()).to.be.bignumber.that.equals(value);
  		});
  	});
  });
  