Understanding Chai's assertions (expect-style)

Question

What's the difference here?

it("should be 5", () => {
  expect(num).equal(5);
});

it("should be 5", () => {
  expect(num).to.be.equal(5);
});

It does not make any difference if I use the first way or the second way. At least it seems so to me.

What's the purpose of the ".to.be."?

Is it just for having something which is more similar to an actual sentence? Or does it something functional?

Answer 1

From the doc

The following are provided as chainable getters to improve the readability of your assertions.

Look this test case:

import { expect } from 'chai';

const num = 5;

describe('62770625', () => {
  it('should be 5', () => {
    expect(num).equal(5);
  });

  it('should be 5', () => {
    expect(num).to.be.equal(5);
  });

  it('should have members', () => {
    expect([{ a: 1 }]).deep.members([{ a: 1 }]); 
    expect([{ a: 1 }]).to.have.deep.members([{ a: 1 }]);
  });
});

Both of them work, but with these language Chains, we can get:

• Better readability
• Human friendly
• Good semantics