How to use the web3-utils.BN function in web3-utils

it("returns correct negative value", function() {
      let bytes = [0xf5, 0xe2, 0xc5, 0x17];  // starts with 0b1
      let raw = new BN("f5e2c517", 16);
      let bitfipped = new BN(
        raw.toString(2)
          .replace(/0/g, "x")
          .replace(/1/g, "0")
          .replace(/x/g, "1"),
        2
      );

      let expectedValue = bitfipped.add(new BN(1)).neg();

      let result = utils.toSignedBN(bytes);

      assert.equal(result.toString(), expectedValue.toString());
    });

const block = await data.contract.interfaceAdapter.getBlock(
        data.receipt.includedInBlock
      );

      // if geth returns null, try again!
      if (!block) return this.postDeploy(data);

      data.timestamp = block.timestamp;

      const balance = new web3Utils.BN(
        await data.contract.interfaceAdapter.getBalance(tx.source)
      );
      const gasUsed = new web3Utils.BN(
        tx.metadata.operation_result.consumed_gas
      );
      const storageUsed = new web3Utils.BN(
        tx.metadata.operation_result.paid_storage_size_diff
      );
      const fee = new web3Utils.BN(tx.fee);
      tx.metadata.operation_result.balance_updates.forEach(
        update => (burn = burn.add(new web3Utils.BN(update.change)))
      );
      burn = burn.abs();
      const value = new web3Utils.BN(tx.balance);
      const cost = fee.add(value).add(burn);

      data.from = tx.source;
      data.balance = web3Utils.fromWei(balance, "mwei");
      data.gasUsed = gasUsed.toString(10);
      data.storageUsed = storageUsed.toString(10);
      data.fee = web3Utils.fromWei(fee, "kwei");
      data.burn = web3Utils.fromWei(burn, "mwei");

constructor (abiType) {
    // skip the "int" part at the start
    let M = abiType.substr(3)
    if (!M.length) {
      M = '256'
    }
    this.maxInt = new BN(2, 10).pow(new BN(M, 10))
    this.minInt = this.maxInt.neg()
  }
  fieldType = () => NUMBER

// if geth returns null, try again!
      if (!block) return this.postDeploy(data);

      data.timestamp = block.timestamp;

      const balance = new web3Utils.BN(
        await data.contract.interfaceAdapter.getBalance(tx.source)
      );
      const gasUsed = new web3Utils.BN(
        tx.metadata.operation_result.consumed_gas
      );
      const storageUsed = new web3Utils.BN(
        tx.metadata.operation_result.paid_storage_size_diff
      );
      const fee = new web3Utils.BN(tx.fee);
      tx.metadata.operation_result.balance_updates.forEach(
        update => (burn = burn.add(new web3Utils.BN(update.change)))
      );
      burn = burn.abs();
      const value = new web3Utils.BN(tx.balance);
      const cost = fee.add(value).add(burn);

      data.from = tx.source;
      data.balance = web3Utils.fromWei(balance, "mwei");
      data.gasUsed = gasUsed.toString(10);
      data.storageUsed = storageUsed.toString(10);
      data.fee = web3Utils.fromWei(fee, "kwei");
      data.burn = web3Utils.fromWei(burn, "mwei");
      data.value = web3Utils.fromWei(value, "mwei");
      data.cost = web3Utils.fromWei(cost, "mwei");

const bn = x => new BN(x)
const bigExp = (x, y) => bn(x).mul(bn(10).pow(bn(y)))

isValid = val => {
    if (Number.isNaN(parseInt(`${val}`, 10))) {
      return false
    }

    try {
      const bv = new BN(`${val}`, 10)
      return bv.gte(this.minInt) && bv.lte(this.maxInt)
    } catch (_) {
      return false
    }
  }
  sanitize = v => (v || '').trim()

constructor(describeJson) {
    this.migrator = null;
    this.deployer = null;
    this.migration = null;
    this.currentGasTotal = new web3Utils.BN(0);
    this.currentCostTotal = new web3Utils.BN(0);
    this.finalCostTotal = new web3Utils.BN(0);
    this.deployments = 0;
    this.separator = "\n";
    this.summary = [];
    this.currentFileIndex = -1;
    this.blockSpinner = null;
    this.currentBlockWait = "";
    this.describeJson = describeJson;

    this.messages = new MigrationsMessages(this);
  }

getTotals() {
    const gas = this.currentGasTotal.clone();
    const cost = web3Utils.fromWei(this.currentCostTotal, "mwei");
    this.finalCostTotal = this.finalCostTotal.add(this.currentCostTotal);

    this.currentGasTotal = new web3Utils.BN(0);
    this.currentCostTotal = new web3Utils.BN(0);

    return {
      gas: gas.toString(10),
      cost: cost,
      finalCost: web3Utils.fromWei(this.finalCostTotal, "mwei"),
      deployments: this.deployments.toString()
    };
  }