expect.js

const assert = require("assert");

// .. code

function expect(actual) {
  return {
    toEqual(expected) {
      assert.equal(actual, expected);
    },
    toBe(expected) {
      assert.deepStrictEqual(actual, expected);
    },
    toBeTruthy() {
      assert.ok(actual);
    },
    toHaveLength(expected) {
      assert.ok(actual.length === expected);
    }
  };
}