jest.spyOn() provide a way to inspect the return value

[evan-scott-zocdoc]

Do you want to request a feature or report a bug?
feature

What is the current behavior?
when something is spied upon, you can see invocation arguments, but not what the return value was

If the current behavior is a bug, please provide the steps to reproduce and either a repl.it demo through https://repl.it/languages/jest or a minimal repository on GitHub that we can yarn install and yarn test.

What is the expected behavior?
something like:

jest.spyOn(window, 'getComputedStyle');

// something

expect(window.getComputedStyle).toHaveReturned(
  expect.objectContaining({
    overflow: 'hidden',
  });
);

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.
jest 19
node 8
npm 5

[maierson]

What is the current way of inspecting return values from spied methods in jest (other than sticking with sinon) ? This is pretty important. I started migrating our tests to jest a few days ago and just ran into it. I'm looking for the equivalent to this (couldn't find with google):

const spy = sinon.spy(instance, "method");
instance.method();
expect(spy.returnValues[0]).to.be.........

[SimenB]

I don't think it's currently possible, at least not mentioned in the docs: https://facebook.github.io/jest/docs/mock-function-api.html

[maierson]

I thought so. Thank you.

[tfiechowski]

If anyone lands here in 2021: it's also possible with mockFn.mock.results. For example:

const apiSpy = jest.spyOn(api, 'list');
const getApiResult = (): Promise<any> => apiSpy.mock.results[0].value;

/* execution/component rendering */

await waitFor(async () =>
  expect(await getApiResult()).toEqual(/* expected result */),
);

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