Provide documentation/support for dynamic mocking of return values in tests

[cebjyre]

Problem

I'd like to have the unit testing of code working with prisma be more precise about what is being passed into and returned from the mocked prisma method. The examples in the documentation make use of mockResolvedValue (with the same data passed into the tested object as is returned by the prisma method) but I'd like to use mockImplementation so I can ensure the prisma method is working with the data that was actually supplied to it.

Suggested solution

Allow (or document if it is already possible) alternative mocking techniques.

Additional context

The suggested mocking solution

test('should create new user ', async () => {
  const user = {
    id: 1,
    name: 'Rich',
    email: '[email protected]',
    acceptTermsAndConditions: true,
  }

  prismaMock.user.create.mockResolvedValue(user)

  await expect(createUser(user)).resolves.toEqual({
    id: 1,
    name: 'Rich',
    email: '[email protected]',
  })
})

would still pass even if the implementation of createUser was:

export async function createUser(user: CreateUser) {
  return await prisma.user.create({
    data: {id: user.id, name: user.name},
  });
}

i.e. the failure by the function to pass the email value down to prisma is not shown by the test.

I've tried using create.mockImplementation but get the equivalent of

Type 'Promise<User>' is missing the following properties from type 'Prisma__UserClient<User>': _dmmf, _fetcher, _queryType, _rootField, and 10 more.

[huv1k]

I would love to see it too, because right now unit testing is really difficult to achieve with more complex problems. Right now there are really simple use-cases possible with unit tests.

[patrykk21]

Same here

[henrikra]

Using mockImplementation works but you have to type the return value of mockImplementation with any 😕

[jkomyno]

We should also document how to mock values within a query extension: prisma/prisma#23394.