How to restore original implementation and continue syping on a method?

[Lordfirespeed]

Title. #3386 is relevant

• mockClear doesn't affect implementation
• mockReset restores an empty implementation (not the original)
• mockRestore stops spying

example:

import { it, vi, afterEach, expect } from "vitest"

const foo = {
  bar: () => "Hello, world!"
}

vi.spyOn(foo, 'bar')

afterEach(() => {
  vi.restoreAllMocks() // the problem area: `restoreAllMocks` un-spies
})

it("Should be spied", () => {
  vi.mocked(foo.bar).mockReturnValue("Placeholder")
  foo.bar()
  expect(foo.bar).toHaveBeenCalled()
})

it("Should still be spied", () => {
  foo.bar()
  expect(foo.bar).toHaveBeenCalled()
})

The first test succeeds, but the second test fails as restoreAllMocks un-spies foo.bar.

How can I restore original implementations after each test, without un-spying?

[sheremet-va]

If you want others to help, you should probably provide some code so it is easier to understand what you mean.

[Lordfirespeed]

Done.

[sheremet-va]

You cannot do that without losing the spy assignment, you need to re-apply the spy again. This is done to be compatible with Jest.

[Lordfirespeed]

I disagree wholeheartedly. It makes very little sense to me that mockRestore would unspy. It's certainly not explicitly mentioned in the docs!

Clearly someone else thought it made sense to have mockRestore keep spies at some point, or #3127 would never have existed.
For example, there are some scenarios where it is not possible to re-apply the spy (e.g. module mocks).

Just to clarify, here is what I am proposing:

import { vi } from "vitest"

const foo = {
    bar: () => "Hello, world!"
}

vi.spyOn(foo, "bar")

vi.mocked(foo.bar).mockRestore({ unspy: false }) // restores original impl without unspying
vi.mocked(foo.bar).mockRestore() // restores original `foo.bar`, unspying

vi.restoreAllMocks({ unspy: false }) // restores original impl for all mocks without unspying
vi.restoreAllMocks() // restores originals for all mocks, unspying

and adding an option e.g. mockRestoreUnspyDefault to the vitest config, true by default.

I don't see why you could possibly have a problem with that - the intent is very obvious. Compatibility with Jest is kept, the library becomes more flexible.

What do you think would make sense instead?

[sheremet-va]

Clearly someone else thought it made sense to have mockRestore keep spies at some point, or #3127 would never have existed.

Someone else (me) introduced a bug that he (me) fixed in #3127

I agree that it is unfortunate when we can't reapply a spy after the mock has been restored.

I think if we want to introduce this behavior, then it should be a separate method. mockRestore correctly removes the spy from the object because it restores the original implementation.

[Lordfirespeed]

Someone else (me) introduced a bug that he (me) fixed in #3127

😂

I think if we want to introduce this behavior, then it should be a separate method. mockRestore correctly removes the spy from the object because it restores the original implementation.

Okay, cool! I'd be plenty happy with that - not sure what to name such a thing, though. We already have mockClear, mockReset, mockRestore. Maybe mockRevert?

[sheremet-va]

mockRever sounds good to me. You can open an issue or a PR for that

[Lordfirespeed]

Opened #6378