[Bug]: spy.mockReset() breaks following mock usage

[alexey-kozlenkov]

Version

29.7.0

Steps to reproduce

0. You write test for function A that calls function B.
1. You want to mock function B for all but one test case
2. You use jest.spy(bModule, 'B').mockImplementation(...) by default
3. In that one specific test case you use spy.mockRestore() to get real implementation
4. Boom! All subsequent test cases fail to use mocked implementation or re-mock it. mockRestore() restored it real hard.

Reproducible case:
https://codesandbox.io/p/sandbox/jest-mock-reset-breaks-future-kk4kjr

1. Open link
2. Run tests

Expected behavior

Able to turn spy to mock implementation in subsequent test cases after test case with mockRestore()

Actual behavior

Unable to get re-mock spy

Additional context

No response

[alexey-kozlenkov]

Ok, I found out that re-creating spy itself after calling .mockRestore() helps. e.g.

  test("calls real sum", () => {
    sumSpy.mockRestore();

    expect(callSum(1, 2)).toBe(3);

    sumSpy = jest.spyOn(sumModule, "sum").mockImplementation(() => 5);
  });

I wonder if this is an expected behaviour or is there a way to keep the spy reference "alive" so that it could be re-mocked without being re-created?