Does anyone have suggestions for efficiently asserting that an `Either<Exception, Any>` with ...

# arrow

[Shalom Halbert]

Does anyone have suggestions for efficiently asserting that an Either<Exception, Any> with left equal to a caught Exception is equal to an expected value?

[simon.vergauwen]

https://github.com/kotest/kotest-extensions-arrow

[simon.vergauwen]

This is a great option if you don’t mind the Kotest assertion dependency.

It allows to rewrite your snippet to:

fun doSomething() = IllegalAccessException().left()

    @Test
    fun sample() {
        val actual = doSomething()
        actual.shouldBeLeft().shouldBeTypeOf<IllegalAccessException>
    }

[simon.vergauwen]

otherwise you could also just do:

assert(actual == expected)

Since Either is implemented as a data class, the problem here is that Throwable is not comparable.
Every constructed Throwable has an unique StackTrace and are thus not equal.

[simon.vergauwen]

assert(RuntimeExeception() != RuntimeExeception())

[Shalom Halbert]

That Kotest extension is perfect, thank you!

[Shalom Halbert]

Ends up shouldBeLeft() is a broken assertion. Added an issue about it:
https://github.com/kotest/kotest-extensions-arrow/issues/99

[simon.vergauwen]

Ooof, you’re correct.
Will create a PR to Kotest to fix asap

[Shalom Halbert]

Glad I could help with identifying it 🙂