Can only call expect.extend(..) once as it overwrites the proxy's custom extend

[sb3700]

Bug

• package version: v1.1.3
• node version: 14.21.3
• npm (or yarn) version: 6.14.18
• jest version: 26.6.2

Relevant code or config

expect.extend({
  toBe1(received) {
    const pass = received === 1;
    return pass
      ? { pass, message: () => `expected ${received} to be 1` }
      : { pass, message: () => `expected ${received} not to be 1` };
  }
});

expect.extend({
  toBe2(received) {
    const pass = received === 2;
    return pass
      ? { pass, message: () => `expected ${received} to be 2` }
      : { pass, message: () => `expected ${received} not to be 2` };
  }
});

console.log(expect['toBe1'], expect['toBe2']);
// [Function (anonymous)] undefined

What happened (please provide anything you think will help):
Thanks for the library!

The problem is at https://github.com/mattphillips/jest-expect-message/blob/main/src/withMessage.js#L92.

expectProxy = Object.assign(expectProxy, expect); overwrites expectProxy.extend with expect.extend.

It could be fixed by changing the line to:

for (const key of expect) {
  if (key !== 'extend') {    // or !(key in eventProxy)
    expectProxy[key] = expect[key];
  }
}

[seggewiss]

Actually expect is not iterable but this would work:

expectProxy.extend = o => {
    expect.extend(o); // add new matchers to expect

    Object.keys(expect).forEach((key) => {
        if (key !== 'extend') {    // or !(key in eventProxy)
            expectProxy[key] = expect[key];
        }
    })
};

I used patch packages locally but will open a MR here hopefully it will be merged 😊