together.js

const MOCK_PRICES = [50, 47, 53, 50, 49, 51, 52];
const MOCK_AVERAGE = 50.29;

global.fetch = jest.fn(() => Promise.resolve({
    json: () => Promise.resolve(MOCK_PRICES)
}));

describe('Gold prices', () => {
    let averagePrice;

    describe('When the average price is called for 7 days', () => {
        beforeEach(async () => {
            averagePrice = await getPricesLastDays(7);
        });

        it('Then the correct average should be returned', () => {
            expect(averagePrice).toEqual({ average: MOCK_AVERAGE });
        });
    });
});