Mocking namespace import function

[JPtenBerge]

Hello fellow Vitesters!

I was hoping you'd be able to help me out with a specific situation. I'm using this namespace import of a function in my code:

import * as walkdir from 'walkdir';

walkdir('some-directory');

And I'm trying to mock this walkdir function call, but this is proving quite tricky so far.

• The docs' cheat sheet has a namespace import example, but not for the scenario where the exported value is the actual function to mock:

  // some-path.ts
  export function method() {}

  import * as exports from 'some-path'
  vi.spyOn(exports, 'method').mockImplementation(() => {})

  Looking at the source code of walkdir, they really set the exported value to a function:

  module.exports = walkdir;
  // ...
  function walkdir(path,options,cb){
  // ...

• Simply trying to return a function with vi.mock() results in an error:

  vi.mock('walkdir', () => { return () => { console.log('hi there'); });

    Error: [vitest] vi.mock(path: string, factory?: () => unknown) is not returning an object. Did you mean to return an object with a "default" key?
  

• From the error, thinking perhaps Vitest magically converts an object with a "default" key

  vi.mock('walkdir', () => {
      return {
          default: {
              get: vi.fn()
          }
      }
  });

  But it doesn't, my production code just receives the object and not a callable function.

• Tried some other stuff like vi.stubGlobal() and vi.spyOn(globalThis, 'walkdir'), but nothing that really yielded anything useful.

So I'm hoping someone here has some insight in how I can make it work. Am I missing something silly? Doing someting else wrong? Is this perhaps just not supported?

Thanks in advance for the help!

[sheremet-va]

In ESM import * as walkdir always returns an object, so it's impossible to call it. Are you sure you don't want to call default export?

[dstotijn]

@sheremet-va Should this example in the API docs be updated to match the ESM interop example you mentioned? E.g. change it to:

vi.mock('path', () => {
  return {
    default: vi.fn(),
    namedExport: vi.fn(),
    // etc...
  }
})

Or is there still a valid use case for default: { myDefaultKey: vi.fn() }? If the docs need to be updated, I can do a quick PR if you like.

[sheremet-va]

@dstotijn I'm not sure what usecase are you talking about? The example in docs is correct.

[dstotijn]

The usage and suggestion you posted in this discussion:

^ This is how CJS<->ESM works in Node. That way you can use vi.mock('path', () => ({ default: vi.fn() }).

[sheremet-va]

The usage and suggestion you posted in this discussion:

^ This is how CJS<->ESM works in Node. That way you can use vi.mock('path', () => ({ default: vi.fn() }).

You can put anything on default, why should we emphasize function? I think object is commonly used.

[dstotijn]

Ah yes, of course! Brain fart on my side. Thanks for clarifying.