Jest mock Knex transaction - node.js

Question

I have the following lambda handler to unit test. It uses a library #org/aws-connection which has a function mysql.getIamConnection which simply returns a knex connection.
Edit: I have added the mysql.getIamConnection function to the bottom of the post
Edit: If possible, I'd like to do the testing with only Jest. That is unless it becomes to complicated
index.js
const {mysql} = require('#org/aws-connection');
exports.handler = async (event) => {
const connection = await mysql.getIamConnection()
let response = {
statusCode: 200,
body: {
message: 'Successful'
}
}
try {
for(const currentMessage of event.Records){
let records = JSON.parse(currentMessage.body);
await connection.transaction(async (trx) => {
await trx
.table('my_table')
.insert(records)
.then(() =>
console.log(`Records inserted into table ${table}`))
.catch((err) => {
console.log(err)
throw err
})
})
}
} catch (e) {
console.error('There was an error while processing', { errorMessage: e})
response = {
statusCode: 400,
body: e
}
} finally {
connection.destroy()
}
return response
}
I have written some unit tests and I'm able to mock the connection.transaction function but I'm having trouble with the trx.select.insert.then.catch functions. H
Here is my testing file
index.test.js
import { handler } from '../src';
const mocks = require('./mocks');
jest.mock('#org/aws-connection', () => ({
mysql: {
getIamConnection: jest.fn(() => ({
transaction: jest.fn(() => ({
table: jest.fn().mockReturnThis(),
insert: jest.fn().mockReturnThis()
})),
table: jest.fn().mockReturnThis(),
insert: jest.fn().mockReturnThis(),
destroy: jest.fn().mockReturnThis()
}))
}
}))
describe('handler', () => {
test('test handler', async () =>{
const response = await handler(mocks.eventSqs)
expect(response.statusCode).toEqual(200)
});
});
This test works partially but it does not cover the trx portion at all. These lines are uncovered
await trx
.table('my_table')
.insert(records)
.then(() =>
console.log(`Records inserted into table ${table}`))
.catch((err) => {
console.log(err)
throw err
})
How can set up my mock #org/aws-connection so that it covers the trx functions as well?
Edit:
mysql.getIamConnection
async function getIamConnection (secretId, dbname) {
const secret = await getSecret(secretId)
const token = await getToken(secret)
let knex
console.log(`Initialzing a connection to ${secret.proxyendpoint}:${secret.port}/${dbname} as ${secret.username}`)
knex = require('knex')(
{
client: 'mysql2',
connection: {
host: secret.proxyendpoint,
user: secret.username,
database: dbname,
port: secret.port,
ssl: 'Amazon RDS',
authPlugins: {
mysql_clear_password: () => () => Buffer.from(token + '\0')
},
connectionLimit: 1
}
}
)
return knex
}
Solution
#qaismakani's answer worked for me. I wrote it slightly differently but the callback was the key. For anyone interested here is my end solution
const mockTrx = {
table: jest.fn().mockReturnThis(),
insert: jest.fn().mockResolvedValue()
}
jest.mock('#org/aws-connection', () => ({
mysql: {
getIamConnection: jest.fn(() => ({
transaction: jest.fn((callback) => callback(mockTrx)),
destroy: jest.fn().mockReturnThis()
}))
}
}))

Answer 1

Updating your mock to look like this might do the trick:
const { mysql } = require("#org/aws-connection");
jest.mock("#org/aws-connection", () => ({
mySql: {
getIamConnection: jest.fn()
}
}));
const mockTrx = {
table: jest.fn().mockReturnThis(),
insert: jest.fn().mockResolveValue() // Resolve any data here
};
mysql.getIamConnection.mockReturnValue({
transaction: jest.fn((callback) => callback(mockTrx)),
});
You need to mock the transaction so that it executes your callback with a dummy trx. To do this, you need to make sure that all the functions inside the trx object return a reference back to it or a promise so that you can chain it appropriately.

Answer 2

Instead of mocking knex implementation, I've written knex-mock-client which allows you to mimic real db with an easy API.
Change your mock implementation with
import { handler } from "../src";
import { getTracker } from "knex-mock-client";
const mocks = require("./mocks");
jest.mock("#org/aws-connection", () => {
const knex = require("knex");
const { MockClient } = require("knex-mock-client");
return {
mysql: {
getIamConnection: () => knex({ client: MockClient }),
},
};
});
describe("handler", () => {
test("test handler", async () => {
const tracker = getTracker();
tracker.on.insert("my_table").responseOnce([23]); // setup's a mock response when inserting into my_table
const response = await handler(mocks.eventSqs);
expect(response.statusCode).toEqual(200);
});
});