Using the `as` operator for mocks in jest tests

When using mocks or spys, and trying to call methods on those, typescript complains that the methods do not exists for those types.

The following can be fixed by forcing typescript to treat those objects as jest.Mock or jest.SpyInstance using the as operator.

import { foo } from 'a/package';

jest.mock('a/package');

// Otherwise TS would throw an error saying mockReturnValue does not exits
const foo = jest.fn() as jest.Mock;
foo.mockReturnValue('some value'); 

// For spies you can use
const mySpy = jest.spyOn(someObject, 'someMethod') as jest.SpyInstance;

Using the as operator for mocks in jest tests

Using the `as` operator for mocks in jest tests