How write simple Jest mock for express-session's req.session.destroy()

Question

I am writing a grapqhl server that has a simple logout mutation. Everything works as expected when I run the server and I can log out by destroying the session and clearing the cookie just fine.

Here is the resolver:

export default async (root, args, context) => {

  console.log("THIS WILL LOG")
  await new Promise((res, rej) =>
    context.req.session.destroy(err => {
      if (err) {
        return rej(false);
      }
      context.res.clearCookie("qid");
      return res(true);
    })
  );
  console.log("NEVER HERE BEFORE TIMEOUT");

  // 4. Return the message
  return {
    code: "OK",
    message: "You have been logged out.",
    success: true,
    item: null
  };
};

I am attempting to write a simple test just to verify that the req.session.destroy and res.clearCookie functions are actually called. At this point I AM NOT attempting to test if a cookie is actually cleared, as I am not actually starting up the server, I am just testing that the graphql resolver was ran correctly and that it called the right functions.

Here is a portion of my test:

describe("confirmLoginResolver", () => {
  test("throws error if logged in", async () => {
    const user = await createTestUser();

    const context = makeTestContext(user.id);
    context.req.session.destroy = jest
      .fn()
      .mockImplementation(() => Promise.resolve(true));
    context.res.clearCookie = jest.fn();

    // this function is just a helper to process my graphql request.
    // it does not actually start up the express server
    const res = await graphqlTestCall(
      LOGOUT_MUTATION, // the graphql mutation stored in a var
      null, // no variables needed for mutation
      null // a way for me to pass in a userID to mock auth state,
      context // Context override, will use above context
    );
    console.log(res);
    expect(context.req.session.destroy).toHaveBeenCalled();
    // expect(res.errors.length).toBe(1);
    // expect(res.errors).toMatchSnapshot();
  });

});

Again, everything works correctly when actually running the server. The problem is that when I attempt to run the above test, I always get a jest timeout:

Timeout - Async callback was not invoked within the 5000ms timeout specified by jest.setTimeout.

The reason is that the await section of above resolver will hang because it's promise.resolve() is never being executed. So my console will show "THIS WILL LOG", but will never get to "NEVER HERE BEFORE TIMEOUT".

I suspect I need to write a better jest mock to more accurately simulate the callback inside of context.req.session.destroy, but I can not figure it out.

Any ideas how I can write a better mock implementation here?

context.req.session.destroy = jest
      .fn()
      .mockImplementation(() => Promise.resolve(true));

Is not cutting it. Thoughts?

Answer 1

Try

context.req.session.destroy = jest
      .fn()
      .mockImplementation((fn) => fn(false));