How to use jest.spyOn with @swc/jest?

[BrunoQuaresma]

I'm trying to use @swc/jest on my project but when I try it I get the following error:

TypeError: Cannot redefine property: deleteTemplate
        at Function.defineProperty (<anonymous>)

jest.spyOn(API, "deleteTemplate")

Thanks in advance!

[magic-akari]

Try this https://www.npmjs.com/package/jest_workaround

[adbutterfield]

I found a pattern that works for a project I'm migrating to swc at work.
Sample here: https://github.com/adbutterfield/fast-refresh-express/blob/main/test/renderHelpers.test.ts

[flora8984461]

I am also stuck on this. The above solutions don't work for me because I am using a 3rd party library that uses swc, and I get this same error. My project does not use swc. jest.mock() with mockReturnedValue and mockImplementation don't use my mock value.

Any suggestions are really appreciated.

[pedenys]

Found by chance a nice and easy workaround that does not involve changing anything in the non-test code (at least for me) :

import * as externallibrary from "external-library";

jest.mock("external-library", () => ({
  __esModule: true,
  ...jest.requireActual("external-library"),
}));

describe("foo tests", () => {

  it("should bar if blop", () => {

    jest.spyOn(externallibrary, "externalMethod").mockReturnValue({
      isAuthenticated: true,
      isLoading: false,
    } as ReturnType<typeof externallibrary.externalMethod>);

   //...
  })
})

Thanks to iarroyo on StackOverflow

[clintonb]

Historical context from #5059: swc "fixed" a bug that enables an invalid use of jest.spyOn.

jest_workaround is now swc_mut_cjs_exports and works well.

I used jest_workaround successfully for many months until a recent change in my repo broke it. I'm still not sure why, but I also realized that I only needed the workaround to resolve issues with a single spy on an exported function. I resolved this by converting the function a static method (which is better for our codebase in the long run), and removing jest_workaround altogether.