ethworks / bn-chai Goto Github PK

Using chai.Assertion.overwriteMethod() it is possible to extend methods like equal, so that we could write

let a = new BN(1);
let b = new BN(1);
expect(a).to.equal(b); //or
a.should.equal(b);

I wrote a minimum viable plugin:

module.exports = function(BN) {
  return function (chai, utils) {
    chai.Assertion.overwriteMethod('equal', function(_super) {
      return function(exp) {
        var obj = utils.flag(this, 'object');
        if (BN.isBN(obj)) {
          chai.assert(obj.eq(exp), "BNs don't equal.");
        } else {
          _super.apply(this, arguments);
        }
      }
    });
  };
};

This extends equal to BNs. However, I don't know how to display the message that was passed and, ideally, to show a diff.
It may also make sense to wrap the expected exp into a new BN(exp) to be more forgiving when passing non-BNs.
Probably, it is cleaner to use something like let test = new Assertion(...); test.assert(...), which I saw in the chai sourcecode, instead of chai.assert(). However, I didn't understand yet how to fill those ...s.

I am using this library after following the upgrade guidelines for the new truffle V5 release, see here: https://github.com/trufflesuite/truffle/releases?after=truffle-code-utils%401.1.2-beta.0

Example code:

const bnChai = require('bn-chai');

// Setup should and bnChai as a plugin
require('chai')
  .use(require('chai-as-promised'))
  .use(bnChai(web3.utils.BN)) // web3 is provided by the test runner in truffle
  .should();

// sample assertion 
myValue.should.be.eq.BN(0);
// gives the following failure: AssertionError: expected 0 to be below 0

When I one of my tests it always outs the following AssertionError: expected 0 to be below 0

Am I using it wrong?

All the equality assertions come out the same way by looking ?