Auto-waiting assertions

[microsoft]

Auto-waiting assertions

[JoelEinbinder]

I had a conversation with @mxschmitt about this offline. Pasting my parts here:

There are a lot of thought provoking ideas in that library, but I am having trouble coming up with a response that covers all of them.

I think we should discuss them individually.
Some should be built into playwright-runner, some into playwright itself, some stay in external libraries.

Like the first example:

await expect(page).toHaveSelector("#foobar");

This is pretty much equivalent to await page.waitForSelector('#foobar') right?

but then

await expect(page).not.toHaveSelector("#foobar");

makes everything a lot trickier

because is this

expect(await page.$('#foobar')).toBe(null);

or is it

expect(await page.waitForSelector('#foobar').catch(e => null)).toBe(null);

one will always wait the full timeout, making the test slow

The other will pass if the element comes in later. So you could have both
expect(page).toHaveSelector and expect(page).not.toHaveSelector pass!

I don't think the "not" case is very important, but staying within the expect syntax forces us to implement it. What if instead it was in playwright itself as a collection of page.assert methods? Then it would also be clearer that expect is synchronous and page.assert is async.

[jperl]

Yes page.assert methods would serve the same purpose as expect, I do not have a strong opinion either way about this.

I can think of a few scenarios where .not.toHaveSelector and .not.toHaveText are valuable.

• After clearing items, to make sure they are gone
• After dismissing a modal, to make sure it is gone

In both of those I would want the test to auto-wait for the selector to be gone. So the test should only be as slow as the application is to remove those elements.

[thernstig]

The text one would be cool to have. An example would be expect(page/element).toHaveText('some text'), taking into account somehow the 3 different kind of text matchers text=example one (case-insensitive, substring matching), text="example 2" (exact matching), text=/^\\s*Some text$/i (regex matching).

Also, I assume the .not.toHaveText('some text') would equal to use waitForSelector('text=some text', {waitFor: 'hidden'})