jest.examples.ts

/////// Mocking dynamoDB

const mockDynamoDbPut = jest.fn();

class DocumentClient {
  put = mockDynamoDbPut;
}

jest.mock('aws-sdk', () => ({
  DynamoDB: {
    DocumentClient,
  },
}));

//..  import { module we want to test } from '.';.//

mockDynamoDbPut.mockImplementation(() => ({ promise: jest.fn() }));

/////// Mocking a function

import { upsert } from './upsert-logic';

jest.mock('./upsert-logic');

const mockUpsert = upsert as jest.MockedFunction<typeof upsert>;
  
mockUpsert.mockResolvedValue('foo')
  
/////// Mocking a class

import { SomeClass } from './SomeClass';

jest.mock('./SomeClass');

const mockedClass = <jest.Mock<SomeClass>>SomeClass;

/////// Mock object
import { mocked } from 'jest-mock';
 const mockedObject = jest.mocked(someObject);