How do you mock typeorm's getManager using testdouble?

Question

When creating unit tests for typeorm, I want to mock my connection to the database so that I can run unit tests without actually ever connecting to the DB (a good thing!)

I see places where people have mocked typeorm's repositories using testdouble (which I am also using), but I am trying to do this with getManager and am having an issue figuring out how to make it work.

Here's an example. I have a class that, in the constructor, creates an EntityManager by using getManager() for a connection called 'test':

export class TestClass {
    constructor() {
        const test: EntityManager = getManager('test');
    }
}

Now I want to test that I can simply create this class. Here's a sample (using mocha, chai, and testdouble):

describe('data transformer tests', () => {
    it('can create the test class', () => {

        // somehow mock getManager here

        const testClass: TestClass = new TestClass();
        chai.expect(testClass, 'could not create TestClass').to.not.be.null;
    });
});

When I try this, I get this error message from typeorm:

ConnectionNotFoundError: Connection "test" was not found.

Here are some of the things I've tried to mock getManager:

td.func(getManager)

same error as above.

td.when(getManager).thenReturn(td.object('EntityMananger'));

gets the message:

Error: testdouble.js - td.when - No test double invocation call detected for `when()`.

Any ideas what the magic sauce is here for mocking getManager?

Answer 1

I tried sinon instead of testdouble. I created a small repository, which shows how you can mock database for your blazing unit-tests :)

I tried to cover all TypeORM test cases using Jest and Mocha

Example

import * as typeorm from 'typeorm'
import { createSandbox, SinonSandbox, createStubInstance } from 'sinon'
import { deepEqual } from 'assert'

class Mock {
  sandbox: SinonSandbox

  constructor(method: string | any, fakeData: any, args?: any) {
    this.sandbox = createSandbox()

    if (args) {
      this.sandbox.stub(typeorm, method).withArgs(args).returns(fakeData)
    } else {
      this.sandbox.stub(typeorm, method).returns(fakeData)
    }
  }

  close() {
    this.sandbox.restore()
  }
}

describe('mocha => typeorm => getManager', () => {
  let mock: Mock

  it('getAll method passed', async () => {
    const fakeManager = createStubInstance(typeorm.EntityManager)
    fakeManager.find.resolves([post])

    mock = new Mock('getManager', fakeManager)

    const result = await postService.getAll()
    deepEqual(result, [post])
  })

  afterEach(() => mock.close())
})