mock module failure

[hax]

Clear and concise description of the problem

Some times we write the conditional logic rely on the result of dynamic import, eg.

export function foo() {
  try {
    const { foo } = await import("foo-lib")
    return foo()
  } catch {
    // fallback
    return fooImpl()
  }
}

function fooImpl() { ... }

To test the logic, we need to mock the module failure. But vi.mock("foo-lib", () => { throw "failure" }) doesn't work. Currently, we use __mock__ file as the workaround, but it's really annoy to add the mock files which only have simple throw statement in them. And it also means we can't use __mock__ files for normal cases.

Suggested solution

Let's introduce a new API to mock module failure: vi.mockFailure(path).

Alternative

No response

Additional context

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[sheremet-va]

That's an interesting issue. I am assuming you experience this issue?

vitest/packages/mocker/src/registry.ts

Line 252 in 8d883cf

'[vitest] There was an error when mocking a module. '

I don't like introducing new methods, but maybe we can add an option to ignore failures. For example:

import { vi } from 'vitest'

vi.mock("foo-lib", { throws: true }, () => { throw "failure" })

[hax]

I am assuming you experience this issue?

Yes.

but maybe we can add an option to ignore failures

I understand the options and factory could provide flexibility so you can mock a module only fails in some conditions. Our case don't need such flexibility so I only proposed a simple method, but yes, options may be a more general solution.