bun:test promise rejection resolves instead of rejects when throw after await with done callback

[Jarred-Sumner]

In the following test, if expect().toBe() fails then the test hangs forever

it("should allow stdout to be read via .read() API", async (done) => {
    const result: string = await new Promise((resolve) => {
      const child = spawn("bun", ["-v"]);
      let finalData = "";
      child.stdout.on("error", (e) => {
        console.error(e);
        done(e);
      });
      child.stdout.on("readable", () => {
        let data;

        while ((data = child.stdout.read()) !== null) {
          finalData += data.toString();
        }
        resolve(finalData);
      });
    });
    expect(SEMVER_REGEX.test(result.trim())).toBe(true);
    done();
});

The reason why is that the Promise handler for test appears to be calling resolve instead of reject.

[mmkal]

I don't know if this is the same bug, but .rejects doesn't seem to work at all. Here's a simpler repro - test passes in jest/playwright but fails in bun:

const action = async (): Promise<unknown> => {
  return Promise.reject(new Error('some error'))
}

test('reject', async () => {
  await expect(action()).rejects.toThrow('some error')
})

[Jarred-Sumner]

As a temporary workaround, can you try putting action() in a function?

const action = async (): Promise<unknown> => {
  return Promise.reject(new Error('some error'))
}

test('reject', async () => {
  await expect(() => action()).rejects.toThrow('some error')
})

[mmkal]

Looks like that works, yes - and in playwright, jest and deno too. Thanks!

[tlgreg]

The last example doesn't seem to be working for me. (bun 0.7.3)
Seems like an issue with the combination of .rejects and .toThrow actually.
If the received is not a function toThrow breaks on that and if it is then rejects fails it on a mismatch.

const action = () => Promise.reject('some error')

test('Promise to be', async () => {
  await expect(Promise.reject('some error')).rejects.toBe('some error')
}) // passes

test('Promise to throw', async () => {
  await expect(action()).rejects.toThrow('some error')
}) // error: Expected value must be a function

test('=> Promise to throw', async () => {
  await expect(action).rejects.toThrow('some error')
}) // error: Expected promise, Received: [Function]

[franciscop]

I just found this after some searching, @tlgreg the current workaround I found is really non-compliant and I documented it in this issue (@Jarred-Sumner feel free to mark as duplicated since I just found this issue):

test("rejects to octopus", () => {
  // This should not be receiving a callback, but it's the only way it works:
  const rejecting = Promise.reject(() => new Error("octopus"));
  return expect(rejecting).rejects.toThrow("octopus");
});

[franciscop]

As a further workaround, this way it can be compatible with both Node.js and Bun (in my case it's a single test that is failing so I've done this until it's fixed upstream):

test("rejects to octopus", () => {
  let rejecting;
  if (typeof Bun !== "undefined") {
    rejecting = Promise.reject(() => new Error("octopus"));
  } else {
    rejecting = Promise.reject(new Error("octopus"));
  }
  return expect(rejecting).rejects.toThrow("octopus");
});

Note another non-compliance bit is that if that first line was let rejecting = Promise.reject(new Error(...)); instead of the else, the test fails, while it should not be failing (a rejected promise that is not awaited for should not be throwing/failing a test).

[lukechilds]

Also hitting this issue and it's blocking our migration since we don't have control of the rejection logic.

[franciscop]

This might be resolved since the related issue is resolved as well:

#4755 (comment)