Jest mock Typeorm Datasource in unit tests (without nestjs) - postgresql

Question

I am working on creating unit tests for a project that uses Typeorm without Nestjs. The file I am creating unit tests for uses queryRunner to start a transaction. My problem is, I am not able to mock the Datasource. I tried multiple ways but the mock is never getting called to replace the actual Datasource that has access to the postgresql database. I saw some solutions to mock it, but they all use Nestjs, which I don't use in my case.
The error I am having in the tests right now is:
Received promise rejected instead of resolved
Rejected to value: [TypeORMError: Driver not Connected]
Any help would be highly appreciated since I'm not an expert in unit tests.
Here's an example of the code that I am having the issue with (replaced some names tho):
datasource.ts
//database config is defined in this file
export const datasource: DataSource = new DataSource(some_config);
dummy.service.ts
export const dummyService = () => {
//datasource is imported from the above file
const queryRunner = datasource.createQueryRunner();
await queryRunner.startTransaction();
try {
const foundObject = await queryRunner.manager.getRepository(MyObject).findOne({
where: { id: someId },
lock: { mode: 'pessimistic_write' },
});
//some more database calls
} catch (error) {
await queryRunner.rollbackTransaction();
} finally {
await queryRunner.release();
}
}
mock.datasource.ts
import { DataSource } from 'typeorm';
export const dataSourceMockFactory: () => MockType<DataSource> = jest.fn(
() => ({
createQueryRunner: jest.fn().mockImplementation(() => ({
connect: jest.fn(),
startTransaction: jest.fn(),
release: jest.fn(),
rollbackTransaction: jest.fn(),
manager: {
getRepository: jest.fn().mockImplementation(() => ({
create: jest.fn(),
findOne: jest.fn(() => {
return getMyDummyObject();
}),
})),
save: jest.fn(),
},
})),
}),
);
export type MockType<T> = {
// eslint-disable-next-line #typescript-eslint/ban-types
[P in keyof T]?: jest.Mock<{}>;
};
dummy.unit.test.ts
describe('dummy service test', () => {
let dataSourceMock: MockType<Typeorm.DataSource>;
beforeEach(async () => {
// This method did not work
jest.mock('typeorm', () => {
const actual = jest.requireActual('typeorm');
return {
...actual,
DataSource: dataSourceMockFactory(),
};
});
// The below method did not work either
jest.mock('./../../db/datasource', () => ({
datasource: dataSourceMockFactory(),
}));
});
afterEach(() => {
jest.clearAllMocks();
});
it('should test dummy service with transaction', async () => {
// getting an error here
await expect(
dummyFunction(),
).resolves.not.toThrow();
});
});