Learning to use jest!

data.json

[
  {
    "id": 1,
    "name": "Chicago Pizza",
    "image": "/images/chicago-pizza.jpg",
    "desc": "The pan in which it is baked gives the pizza its characteristically high edge which provides ample space for large amounts of cheese and a chunky tomato sauce.",
    "price": 9
  },
  {
    "id": 2,
    "name": "Neapolitan Pizza",
    "image": "/images/neapolitan-pizza.jpg",
    "desc": "This style of pizza is prepared with simple and fresh ingredients: a basic dough, raw tomatoes, fresh mozzarella cheese, fresh basil, and olive oil. A fantastic original pizza.",
    "price": 7
  },
  {
    "id": 3,
    "name": "New York Pizza",
    "image": "/images/ny-pizza.jpg",
    "desc": "New York-style pizza has slices that are large and wide with a thin crust that is foldable yet crispy. It is traditionally topped with tomato sauce and mozzarella cheese.",
    "price": 8
  },
  {
    "id": 4,
    "name": "Sicilian Pizza",
    "image": "/images/sicilian-pizza.jpg",
    "desc": "Sicilian pizza is pizza prepared in a manner that originated in Sicily, Italy. Sicilian pizza is also known as sfincione or focaccia with toppings. A great tasteful pizza all around.",
    "price": 9
  }
]

ZeroToHero.spec.js

import pizzas from '../data.json';

test('pizza data is correct ', () => {
  expect(pizzas).toMatchSnapshot();
  expect(pizzas).toHaveLength(4);
  expect(pizzas.map(pizza => pizza.name)).toEqual([
    'Chicago Pizza',
    'Neapolitan Pizza',
    'New York Pizza',
    'Sicilian Pizza'
  ])
})

for (let i = 0; i < pizzas.length; i++) {
  test(`pizza[${i}] should have (id, name, image, desc, price)`, () => {
    expect(pizzas[i]).toHaveProperty('id');
    expect(pizzas[i]).toHaveProperty('name');
    expect(pizzas[i]).toHaveProperty('image');
    expect(pizzas[i]).toHaveProperty('desc');
    expect(pizzas[i]).toHaveProperty('price');
  });
}


test('mock imp of basic funtion ', () => {
  const mock = jest.fn(() => 'Im a mock function');
  expect(mock('calling my mock function')).toBe('Im a mock function')
  expect(mock).toHaveBeenCalledWith('calling my mock function')
})


test('mock return value of func one time', () => {
  const mock =jest.fn();

  mock.mockReturnValueOnce('Hello')
  .mockReturnValueOnce('There')

  mock();
  mock();

  expect(mock).toHaveBeenCalledTimes(2);

  mock('Hello', 'There', 'Steve');
  expect(mock).toHaveBeenCalledWith('Hello','There','Steve')

  mock('Steve');
  expect(mock).toHaveBeenLastCalledWith('Steve');  
})


test('mock imp of function ', () => {
  const mock = jest.fn().mockImplementation(() => 'United Kingdom');
  expect(mock('Location')).toBe('United Kingdom');
  expect(mock).toHaveBeenCalledWith('Location');
})


test('spying using og imp', () => {
  const pizza={
    name: n =>`Pizza name: ${n}`
  };

  const spy = jest.spyOn(pizza, 'name');
  expect(pizza.name('Cheese')).toBe('Pizza name: Cheese')
  expect(spy).toHaveBeenCalledWith('Cheese');
})


test('spying using mock imp', () => {
  const pizza={
    name: n =>`Pizza name: ${n}`
  };

  const spy = jest.spyOn(pizza, 'name');
  spy.mockImplementation(n => `crazy pizza`)

  expect(pizza.name('Cheese')).toBe('crazy pizza')
  spy.mockRestore();
  expect(pizza.name('Cheese')).toBe('Pizza name: Cheese');
})

test('pizza returns new york last', () => {
  const pizza0 = pizzas[0]
  const pizza1 = pizzas[1]
  const pizza2 = pizzas[2]
  const pizza = jest.fn(currentPizza => currentPizza.name);

  pizza(pizza0);
  pizza(pizza1);
  pizza(pizza2);
  
  expect(pizza).toHaveLastReturnedWith('New York Pizza')
})

test('pizza data has new york pizza and is a object', () => {
  const newYorkPizza ={
    "id": 3,
    "name": "New York Pizza",
    "image": "/images/ny-pizza.jpg",
    "desc": "New York-style pizza has slices that are large and wide with a thin crust that is foldable yet crispy. It is traditionally topped with tomato sauce and mozzarella cheese.",
    "price": 8
  }

  expect(pizzas[2]).toMatchObject(newYorkPizza);
})


test('expect promise to resolve', async () => {
  const user ={
    getFullName: jest.fn(()=> Promise.resolve('Karl Hadwen'))
  };

  await expect(user.getFullName('Karl Hadwen')).resolves.toBe('Karl Hadwen')
})


test('expect promise to reject', async () => {
  const user ={
    getFullName: jest.fn(()=> Promise.reject(new Error('something is terribly wrong')))
  };

  await expect(user.getFullName('Karl Hadwen')).rejects.toThrow('something is terribly wrong')
})