beOneOf doesn't tell you what value it was.

[busches]

When using beOneOf, it doesn't tell you what it was if it's (not) in the collection.

Example:
1 shouldBeOneOf listOf(2, 3)

Error:
Collection should contain the instance of value, but doesn't.

Suggested output:
<Value> was expected to be in the collection of <Collection>, but wasn't.
<Value> was not expected to be in the collection of <Collection>, but was.

Tested against 4.6.3, but from looking at master, looks like it hasn't been changed in 5.x -

kotest/kotest-assertions/kotest-assertions-core/src/commonMain/kotlin/io/kotest/matchers/collections/oneof.kt

Lines 84 to 96 in 375c1a6

	fun <T> beOneOf(collection: Collection<T>) = object : Matcher<T> {
	override fun test(value: T): MatcherResult {
	if (collection.isEmpty()) throwEmptyCollectionError()
	val match = collection.any { it === value }
	return MatcherResult(
	match,
	{ "Collection should contain the instance of value, but doesn't." },
	{
	"Collection should not contain the instance of value, but does."
	})
	}
	}

[busches]

Well, I think this is more my mistake as I wanted to use beIn at the end, which does have the nice error messages. I'll leave it up to you if you still think this makes sense.

[sksamuel]

Thanks for the idea. Updated in main branch.