Jest mocking a module with module pattern and having unique functionality on each test-CodePudding

I'm having trouble having a unique implementation of search from this module pattern setup I have (MyConnection.js) - here's similar to what I have:

// MyConnection.js
const MyConnection = () => {
  const search = async (q) => {
    //...some functionality
  };
  return {
    search,
  };
};
  

//JEST TESTS
const MyConnection = require('../MyConnection')

// this works - but it sets the search implementation 
// for the whole test file I believe
jest.mock('../MyConnection', () => {
    return jest.fn(()=>{
        search: ()=> ['mocked', 'fn', 'results']
    })
})


//the jest tests - I want different 
// implementations of search in each test
describe('connection tests', ()=>{

    it('test one', ()=>{

        //Not sure if its something like this to set 'search' for each test? This doesn't work as is
        MyConnection.search.mockImplementation((q)=>{`You searched ${q}`})
    })

    it('test two', ()=>{
        MyConnection.search.mockImplementation((q)={q.length>32? 'a': 'b' }})
    })

})

How can I get unique Jest mock implementations of that search function for each test?

CodePudding user response：

You should make sure that mock MyConnection always returns the same connection object in your test file and the module you want to test.

MyConnection.js:

const MyConnection = () => {
  const search = async (q) => {};
  return {
    search,
  };
};

module.exports = MyConnection;

main.js:

const MyConnection = require('./MyConnection');

async function main(q) {
  const conn = MyConnection();
  return conn.search(q);
}

module.exports = main;

main.test.js:

const MyConnection = require('./MyConnection');
const main = require('./main');

jest.mock('./MyConnection', () => {
  console.log('MyConnection module gets mocked');
  const conn = { search: jest.fn() };
  return jest.fn(() => conn);
});
const mConn = MyConnection();

describe('connection tests', () => {
  it('test one', async () => {
    mConn.search.mockImplementation((q) => {
      return `You searched ${q}`;
    });
    const actual = await main('teresa teng');
    expect(actual).toBe('You searched teresa teng');
  });

  it('test two', async () => {
    mConn.search.mockImplementation((q) => {
      return q.length > 32 ? 'a' : 'b';
    });
    const actual = await main('_');
    expect(actual).toBe('b');
  });
});

test result:

 PASS  examples/70132655/main.test.js (10.454 s)
  connection tests
    ✓ test one (2 ms)
    ✓ test two (1 ms)

  console.log
    MyConnection module gets mocked

      at examples/70132655/main.test.js:5:11

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        10.903 s

You can't mock it like this:

jest.mock('./MyConnection', () => {
  console.log('MyConnection module gets mocked');
  return jest.fn(() => { search: jest.fn() });
});

Why? Because every time you call the MyConnection() function in the test file or the file you want to test. It will return a new mock object({ search: jest.fn() }), the mock objects in file under test and test case are not same.