ReferenceError: Cannot access 'myMock' before initialization if test itself and 'myMock' are in different files

[dbtrnl]

🐛 Bug Report

Same problem as issue #10996, encountering ReferenceError: Cannot access 'myMock' before initialization while trying to run test on a mock imported from another file.
If the mock is in the same file as the test, it runs correctly.

These two test cases are included in the repo (see below)

To Reproduce

1. Clone the repo https://github.com/dnbtr/jest-test-bug;
2. Run $ npm install to install dependencies;
3. Run tests with $ npm test.

Expected behavior

Two tests are provided, in the following folders:
src/tests/workingTest
src/tests/buggyTest

Files on src/adapters and src/integrations are not relevant to the issue.
I hadn't time to cut the code to the bare minimum.

The workingTest should pass, the buggyTest should fail with ReferenceError: Cannot access 'mockDynamoRepository_1' before initialization.

Both tests are identical, the difference is that the mock (DynamoRepositoryMock) was moved to a different file in the buggy test.
Uncomment lines on src/tests/buggyTest/buggyTest.spec.ts to see other implementations that also don't work and result in the same error.

Expected output:

 PASS  src/tests/workingTest/workingTest.spec.ts (6.316 s)
 FAIL  src/tests/buggyTest/buggyTest.spec.ts
  ● Test suite failed to run

    ReferenceError: Cannot access 'mockDynamoRepository_1' before initialization

      17 | // jest.mock('aws-sdk', () => { mockDynamoRepository; });
      18 |
    > 19 | jest.mock('aws-sdk', () => mockDynamoRepository<TestType>([]));
         |                                                ^
      20 |
      21 | describe('Test DynamoRepository (buggy test, SHOULD FAIL)', () => {
      22 |   const repo: IRepositoryAdapter = DynamoRepository;

      at src/tests/buggyTest/buggyTest.spec.ts:19:48
      at Object.<anonymous> (src/integrations/DynamoRepository.ts:5:1)
      at Object.<anonymous> (src/tests/buggyTest/buggyTest.spec.ts:3:1)

Link to repo

https://github.com/dnbtr/jest-test-bug

envinfo

There is no env. Repo can be used as-is.

[ahnpnl]

Does it happen if you use babel-jest to transform TypeScript (I see you are using ts-jest)?

[dbtrnl]

Hello,

I tried babel-jest using the instructions in Jest's README, but the error persists. I created a new branch for reproduction.

Tried calling jest with different parameters as well (see 'package.json`) but always the same result.

[SimenB]

This is a runtime error, the babel plugin would have warned you if you didn't name it mock*. You need to do require or something inside the jest.mock callback. jest.mock calls are hoisted, so they run before you import the helper, and thus the helper is not yet defined when you try to use it

[dbtrnl]

Hi Simen,

Strangely, the mock had a different name (without mock*), but there were no warnings, which led me to opening this issue.
I changed it to the current name because of the issue referenced in the beginning.

I still can't quite make it function, but now it's a Typescript thing. Thanks for the help.

[SimenB]

Ah, probably because of ts-jest's implementation of the hoisting.

Using babel-jest throws this:

[dbtrnl]

I see, thanks for the insight! I still get lost on the internals of Jest :(

[github-actions]

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