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

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.

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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.

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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

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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.

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You could replace it() with xit() to temporarily exclude a test from being executed; using it() and xit() is more eloquent than using test() and xit().

see Focusing and Excluding Tests

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The following is an excerpt from the document：link

test(name, fn, timeout) Also under the alias: it(name, fn, timeout) All you need in a test file is the test method which runs a test. For example, let's say there's a function inchesOfRain() that should be zero. Your whole test could be: ......

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Jest haven't mentioned why they have two versions for the exact same functionality.

My guess is, it's only for convention. test is for unit tests, and it is for integration tests.

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They are the same thing. I am using TypeScript as the programming language, and when I look into the definition file from the Jest package source code from /@types/jest/index.d.ts, I can see the following code.

Obviously, there are lots of different names of 'test', and you can use any of them.

declare var beforeAll: jest.Lifecycle; declare var beforeEach: jest.Lifecycle; declare var afterAll: jest.Lifecycle; declare var afterEach: jest.Lifecycle; declare var describe: jest.Describe; declare var fdescribe: jest.Describe; declare var xdescribe: jest.Describe; declare var it: jest.It; declare var fit: jest.It; declare var xit: jest.It; declare var test: jest.It; declare var xtest: jest.It;

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