Example 1: jest test array of objects
const users = [{id: 1, name: 'Hugo'}, {id: 2, name: 'Francesco'}];
test('we should have ids 1 and 2', () => {
expect(users).toEqual(
expect.arrayContaining([
expect.objectContaining({id: 1}),
expect.objectContaining({id: 2})
])
);
});
Example 2: simple jest test cases for array of objects
import pizzas from '../data';
// very basic test to notify the user if our pizza data has changed
test('the 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',
]);
});
// let's test that each item in the pizza data has the correct properties
for (let i = 0; i < pizzas.length; i += 1) {
it(`pizza[${i}] should have properties (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');
});
}
// default jest mock function
test('mock implementation of a basic function', () => {
const mock = jest.fn(() => 'I am a mock function');
expect(mock('Calling my mock function!')).toBe('I am a mock function');
expect(mock).toHaveBeenCalledWith('Calling my mock function!');
});
// let's mock the return value and test calls
test('mock return value of a function one time', () => {
const mock = jest.fn();
// we can chain these!
mock.mockReturnValueOnce('Hello').mockReturnValueOnce('there!');
mock(); // first call 'Hello'
mock(); // second call 'there!'
expect(mock).toHaveBeenCalledTimes(2); // we know it's been called two times
mock('Hello', 'there', 'Steve'); // call it with 3 different arguments
expect(mock).toHaveBeenCalledWith('Hello', 'there', 'Steve');
mock('Steve'); // called with 1 argument
expect(mock).toHaveBeenLastCalledWith('Steve');
});
// let's mock the return value
// difference between mockReturnValue & mockImplementation
test('mock implementation of a function', () => {
const mock = jest.fn().mockImplementation(() => 'United Kingdom');
expect(mock('Location')).toBe('United Kingdom');
expect(mock).toHaveBeenCalledWith('Location');
});
// spying on a single function of an imported module, we can spy on its usage
// by default the original function gets called, we can change this
test('spying using original implementation', () => {
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');
});
// we can mock the implementation of a function from a module
test('spying using mockImplementation', () => {
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(); // back to original implementation
expect(pizza.name('Cheese')).toBe('Pizza name: Cheese');
});
// let's test pizza return output
test('pizza returns new york pizza last', () => {
const pizza1 = pizzas[0];
const pizza2 = pizzas[1];
const pizza3 = pizzas[2];
const pizza = jest.fn(currentPizza => currentPizza.name);
pizza(pizza1); // chicago pizza
pizza(pizza2); // neapolitan pizza
pizza(pizza3); // new york pizza
expect(pizza).toHaveLastReturnedWith('New York Pizza');
});
// let's match some data against our object
test('pizza data has new york pizza and matches as an 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);
});
// async example, always return a promise (can switch out resolves with reject)
test('expect a 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 a promise to reject', async () => {
const user = {
getFullName: jest.fn(() =>
Promise.reject(new Error('Something went wrong'))
),
};
await expect(user.getFullName('Karl Hadwen')).rejects.toThrow(
'Something went wrong'
);
});