We will now explore testing functions that return a Promise. Let’s return to the findRecipe() function altered slightly. Instead of passing the fetched data to a callback, the function will now return a Promise. We now can use this function, along with the await keyword, like so:

const recipe = await findRecipe('pesto');
console.log(recipe);
/* 
Prints {
  'Basil': '2 cups',
  'Pine Nuts': '2 tablespoons',
  'Garlic': '2 cloves',
  'Olive Oil': '0.5 cups',
  'Grated Parmesan': '0.5 cups'
}
*/

Jest supports the use of the async and await keywords, making handling Promises a breeze! Our test for the findRecipe() function can now be written like so:

test("get the full recipe for pesto", async () => {
  //arrange
  const dish = "Pesto"
  const expectedRecipe = {
    'Basil': '2 cups',
    'Pine Nuts': '2 tablespoons',
    'Garlic': '2 cloves',
    'Olive Oil': '0.5 cups',
    'Grated Parmesan': '0.5 cups'
  }

  //act  
  const actualRecipe = await findRecipe(dish);

  //assertion
  expect(actualRecipe).toEqual(expectedRecipe);
});

Remember, when using the async and await keywords, the async keyword is placed before the function that contains asynchronous code. In this case, that would be the callback passed to test(). Then, the await keyword is placed in front of the asynchronous function call findRecipe().

With the inclusion of the async/await keywords, Jest will wait for any await statement to resolve before continuing on.