BigInt support (mocha v8.3+)

[chharvey]

Original comment:

I’m getting this issue with Node.js’s built-in assert.strictEqual function only when using with Mocha.

When running Node (v14.15.0) on the command line,

assert.strictEqual(0n, 1n);

I get the error:

Uncaught AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:

0n !== 1n

This is as expected, as the error reports what it should report.

But when running in Mocha (with gulp and ts-node):

import * as assert from 'assert'; // Node.js

describe('module', () => {
   it('test', () => {
      assert.strictEqual(0n, 1n);
   });
});

TypeError: Do not know how to serialize a BigInt
at JSON.stringify (<anonymous>)
at processImmediate (internal/timers.js:461:21)

Any idea why assert.strictEqual runs differently in Mocha than in the Node.js REPL?

Configurations: (click to expand)

Gulp file:

function test() {
	return gulp.src('./test/**/*.ts')
		.pipe(mocha({
			require: 'ts-node/register',
		}))
}

NPM dependencies:

  "devDependencies": {
    "@types/mocha": "^8.0.0",
    "@types/node": "^14.0.1",
    "gulp": "^4.0.2",
    "gulp-mocha": "^7.0.2",
    "gulp-typescript": "^5.0.1",
    "ts-node": "^9.0.0",
    "typescript": "~4.0.3"
  },

This seems to be fixed with mochajs/mocha#4112, but that is in mocha v8.3.0, and this project only uses version ^6. I tried submitting a PR to retroactively apply the fix to v6, but they denied saying that LTS is not pursued.

One possible solution to this issue would be to upgrade to mocha ^8.3.