Does Kotest have the equivalent of AssertJ's `extr...

# kotest

[Klitos Kyriacou]

Does Kotest have the equivalent of AssertJ's extracting feature? For example, in AssertJ I can do this:

assertThat(foo)
    .extracting(Foo::id, Foo::description)
    .containsExactly(1234, "this is a foo")

The closest I could find was shouldBeEqualUsingFields but that's not suitable, as it requires another Foo argument which I can't easily construct; I only have the naked property values.

[Jim]

I'd do:

all(foo) {
  it.id shouldBe 1234
  it.description shouldBe "stuff"
}

[LeoColman]

I'd go with

assertSoftly(foo) {
    it.id shouldBe 1234
    it.description shouldBe "stuff"
}

[LeoColman]

This way you'd get every failing assertion

[Jim]

Yeah all ~= assertSoftly

[Emil Kantis]

Agree,, but you don't need to use it iirc? the assertSoftly should lambda should already be scoped to the subject?

[Jim]

Yeah I couldn't remember if all was T.() -> Unit or (T) -> Unit 🤪

[Jim]

It might even be T.(T) I've seen that here and there

[Emil Kantis]

Funny, yeah it seems to be

[Emil Kantis]

test("hello") {
         val p = Point(0.0, 3.0)
         assertSoftly(p) {
            x shouldBeGreaterThan -1.0
            it.y shouldBe 3.0
         }
      }

[Jim]

I like both, since you have access to the lambda arg you can destructure a pair or something with a useful name

[sam]

(T).T -> is a bizarre signature lol

[Emil Kantis]

good point @Jim 🙂

[Klitos Kyriacou]

Yes, you can do that, but then the assertion failure message is something like "expecting 123 to be 456". The advantage of AssertJ's extracting method is that it tells you "expecting id to be 456 but was 123." Much clearer and much more helpful.

[Jim]

Maybe a reflection powered assertion could get us there with an auto clue

[LeoColman]

(T).T -> is a bizarre signature lol

"I want T both as a receiver and as a parameter".

The only way to do it really is crying before, hence the T_T

[Emil Kantis]

assertProperties(p) {
  Point::x shouldBe 0.0
  Point::y shouldBe 3.0
}

doable? @Jim? 🙂

[Jim]

I think I did something like this at work, let me see

[sam]

We should add a compiler plugin that is better with shouldBe

[sam]

so x shouldBe y can capture the variable name on the left

[sam]

There's power assert, which is cool because it builds a tree of the intermediate values, but I think we could get half way there with something quicker that just captures the variable names, which is mostly what I want to see.

[Jim]

fun isOdd(x: Int) = x % 2 != 0

data class IntWrapper(val value: Int) {
    fun isOddWrapper() = isOdd(value)
}

class SampleTests : FunSpec({
    test("function pointer") {
        all(IntWrapper(1)) {
            its { ::isOddWrapper } shouldBe false
            its { ::isOdd } shouldBe false
        }
    }
})

data class ShouldBeLeft<R>(val name: String, val actual: R) {
    infix fun shouldBe(expected: R) {
        withClue("Expected property $name to equal $expected but was $actual") {
            actual shouldBe expected
        }
    }
}

infix fun <T, R> T.its(kfunc: (T) -> KFunction<R>): ShouldBeLeft<R> {
    val f = kfunc(this)

    return if ((f as? FunctionReferenceImpl)?.boundReceiver != null) {
        ShouldBeLeft(f.name, f.call())
    } else {
        ShouldBeLeft(f.name, f.call(this))
    }
}

[Jim]

damn, too slow 😂

[Jim]

Expected property isOddWrapper to equal false but was true
java.lang.AssertionError: Expected property isOddWrapper to equal false but was true
expected:<false> but was:<true>

[Jim]

only works with JVM I think though