Is there some way to make a suspending call within...

# kotest

[Vampire]

Is there some way to make a suspending call within a custom matcher?
Something like

fun beValid(): Matcher<PathLike> {
    return Matcher { path ->
        MatcherResult(
            validate(YAML.parse(readFile(path, utf8))),
            { "..." },
            { "..." }
        )
    }
}

just in working

[LeoColman]

What is the suspend call here? validate?

[LeoColman]

Or is it inside the message?

[LeoColman]

I'd say you can probably just make your matchers suspend and call it inside a kotest spec, which should handle suspend functions seamlessly

[Vampire]

readFile is the suspending call

[Vampire]

Right now I have readFile(path.join(dataDir, "foo.yml"), utf8) should beValid() but it would be nicer to have path.join(dataDir, "foo.yml") should beValid().

[Vampire]

If I make the beValid() suspend, this does not help as I need the data argument for the suspending call.
And the Matcher.invoke does not take a suspending function.

[Vampire]

And Matcher.test is also not suspending

[Emil Kantis]

Can't you move the readFile outside of the matcher? I.e
path should beValid() -> readFile(path) should beValid()

[Vampire]

That's what I have and would like to change as it is (hopefully) unnecessary repetition in each assertion line. :-)

[phldavies]

alternatively, have a suspend fun PathLike.shouldBeValid() { readFile(this, utf8) should beValid() } helper to make it nicer at the callsite - i.e. path.shouldBeValid()

[LeoColman]

And Matcher.test is also not suspending

I wonder why it isn't. I think it probably should be.
@sam?

[sam]

Cos the assertions were built before coroutines existed

[sam]

And becuase we wanted them usable in junit

[Vampire]

So I take it is not possible, thanks.
But the suspending shouldBeValid is a nice idea, thanks.

[phldavies]

would a SuspendingMatcher type and equivalent suspend infix fun <T> T.should(matcher: SuspendingMatcher<T>) be useful for those assertions? only usable from a suspend callsite of course (so no junit)

[sam]

would have to check that the type inference picks up the right should, since the other should accepts an Any, but if it does then that would be a clever way of allowing suspending matchers

[Vampire]

In this case the function is really nice, because I can also move the join call inside.
So now it is just "foo.yml".shouldBeValid() with

private suspend fun String.shouldBeValid(dataDir: String = goodDir): String {
    readFile(path.join(dataDir, this), utf8) should beValid()
    return this
}

private suspend fun String.shouldNotBeValid(dataDir: String = badDir): String {
    readFile(path.join(dataDir, this), utf8) shouldNot beValid()
    return this
}

(the parameters are mostly just for now when testing intentional test failure to see the proper error messages. 🙂)

[Vampire]

But for other use-cases the SuspendingMatcher might indeed be helpful

[Vampire]

Type inference should hopefully indeed pick up the right should as SuspendingMatcher is more specific than Any.
Besides that as far as I can see should accepts Matcher, not Any, but other than that it should be the same.

[sam]

oh yeah its shouldBe that is Any not should