What is the difference between 'it' and 'test' in Jest?

As the other answers have clarified, they do the same thing.

I believe the two are offered to allow for either 1) "RSpec" style tests like:

const myBeverage = {
  delicious: true,
  sour: false,
};

describe('my beverage', () => {
  it('is delicious', () => {
    expect(myBeverage.delicious).toBeTruthy();
  });

  it('is not sour', () => {
    expect(myBeverage.sour).toBeFalsy();
  });
});

or 2) "xUnit" style tests like:

function sum(a, b) {
  return a + b;
}

test('sum adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

Documentation:

• https://jestjs.io/docs/en/api.html#describename-fn
• https://jestjs.io/docs/en/api.html#testname-fn-timeout

They do the same thing, but their names are different and with that their interaction with the name of the test.

test

What you write:

describe('yourModule', () => {
  test('if it does this thing', () => {});
  test('if it does the other thing', () => {});
});

What you get if something fails:

yourModule > if it does this thing

it

What you write:

describe('yourModule', () => {
  it('should do this thing', () => {});
  it('should do the other thing', () => {});
});

What you get if something fails:

yourModule > should do this thing

So it's about readability not about functionality.

In my opinion, it really has a point when it comes to read the result of a failing test that you haven't written yourself. It helps to faster understand what the test is about.

Some developer also shorten the Should do this thing to Does this thing which is a bit shorter and also fits semantically to the it notation.

As the jest documentation says, they are the same: it alias

test(name, fn, timeout)

Also under the alias: it(name, fn, timeout)

And describe is just for when you prefer your tests to be organized into groups: describe

describe(name, fn)

describe(name, fn) creates a block that groups together several related tests. For example, if you have a myBeverage object that is supposed to be delicious but not sour, you could test it with:

const myBeverage = {
  delicious: true,
  sour: false,
};

describe('my beverage', () => {
  test('is delicious', () => {
    expect(myBeverage.delicious).toBeTruthy();
  });

  test('is not sour', () => {
    expect(myBeverage.sour).toBeFalsy();
  });
});

This isn't required - you can write the test blocks directly at the top level. But this can be handy if you prefer your tests to be organized into groups.

The Jest docs state it is an alias of test. So they are exactly the same from a functional point of view. They exist both to enable to make a readable English sentence from your test.