I have a pretty simple module that use pg
(node-postgre
lib) module,
I'd like to implement a Jest test and while mocking the pg
module I would like to run it's callback function to see the console.log
runs and my callback is being invoked
I have mocked the module and tried to spy and replace the 'query' method but it failed and crushed, any Idea what am I doing wrong?
Test Subject:
import {Pool} from 'pg';
const pool = new Pool();
module.exports = {
query: (text, params, callback) => {
const start = Date.now();
return pool.query(text, params, (err, res) => {
const duration = Date.now() - start;
console.log('executed query', {text, duration, rows: res.rowCount});
callback(err, res);
});
}
};
Test:
jest.mock('pg');
import module from './index';
import { Pool } from 'pg'
beforeAll(() => {
Pool.mockImplementation(()=>{return jest.fn()});
});
it('callback is called', () => {
const cb = (err, res) => true;
const query = jest.spyOn(Pool, "query"); // <---- Not right, Error
query.mockImplementation((a,b,c) => c({},{}));
const resolve = module.query('QUERY TEXT', { a: 1, b: 2}, cb);
resolve(); // <---- Not what I expect
expect(cb).toBeCalled();
});
});
Error thrown: Error: Cannot spy the query property because it is not a function; undefined given instead
20 | it('callback is called', () => {
21 | const cb = (err, res) => true;
> 22 | const query = jest.spyOn(Pool, "query");
| ^
23 | query.mockImplementation((a,b,c) => c({},{}));
24 | const resolve = module.query('QUERY TEXT', { a: 1, b: 2}, cb);
25 | resolve();
at ModuleMockerClass.spyOn (node_modules/jest-mock/build/index.js:697:15)
at Object.spyOn (src/db/index.test.js:22:24)
Thanks
Here is the unit test solution:
index.js
:
import { Pool } from 'pg';
const pool = new Pool();
module.exports = {
query: (text, params, callback) => {
const start = Date.now();
return pool.query(text, params, (err, res) => {
const duration = Date.now() - start;
console.log('executed query', { text, duration, rows: res.rowCount });
callback(err, res);
});
}
};
index.spec.js
:
import mod from '.';
import { Pool } from 'pg';
jest.mock('pg', () => {
const mPool = {
query: jest.fn()
};
return { Pool: jest.fn(() => mPool) };
});
const pool = new Pool();
afterEach(() => {
jest.resetAllMocks();
jest.restoreAllMocks();
});
it('callback is called', done => {
let queryCallback;
pool.query.mockImplementation((text, params, callback) => {
queryCallback = callback;
});
const logSpy = jest.spyOn(console, 'log');
const userCallback = jest.fn();
mod.query('text', 'params', userCallback);
const mRes = { rowCount: 1 };
queryCallback(null, mRes);
expect(pool.query).toBeCalledWith('text', 'params', queryCallback);
expect(userCallback).toBeCalledWith(null, mRes);
expect(logSpy).toBeCalledWith('executed query', { text: 'text', duration: expect.any(Number), rows: 1 });
done();
});
Unit test result with 100% coverage:
PASS src/stackoverflow/52831401/index.spec.js
✓ callback is called (15ms)
console.log node_modules/jest-mock/build/index.js:860
executed query { text: 'text', duration: 0, rows: 1 }
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 100 | 100 | |
index.js | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 4.026s
Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/52831401