Is there any way to add custom methods to assert interface of chai?

Question

Is there any way to add custom methods to assert interface of chai?

I've tried with:

// test-helper.js

export const testPlugin = function(chai) {
    chai.Assertion.addMethod('customMethod', function() {
      //Something
    })
 }

// abc.test.js

import {assert, use} from 'chai'
import {testPlugin} from 'test-helper.js'

use(testPlugin)

But I think this only works for the expect interface of chai. I want to use this custom method as assert.customMethod(actual, expected)

Let me know if I am missing something here.

Answer 1

Expanding the other answer... look at the definition for Chai's assert.equal and the other native assertions for reference. Your custom assertion might look like:

const chai = require("chai");
chai.assert.assertSpecial = function (actual) {
    // see https://github.com/chaijs/chai/blob/master/lib/chai/assertion.js
    // for Assertion's argument definitions
    const test = new chai.Assertion(null, null, chai.assert, true);
    test.assert(
        actual === "special",
        `expected ${actual} to be "special"`,
        `expected ${actual} to not be "special"`,
        "special",
        actual,
        true);
};