I am currently migrating some groovy tests to kotlin. With that I want to write a kotlin (extension?) function to set an immutable property by name with a given value in my constructor. So I have a variable which includes a property name and a variable which includes so if you have a data class:

data class Foo(val id: Int? = null, val someStringProperty: String? = null)

I would like to write something like

createFoo(propertyName: String, propertyValue: Any): Foo

which I can then use like:

val foo1 = createFoo("id", 5) // Foo(id = 5, someStringProperty = null)
val foo2 = createFoo("someStringProperty", "someString") // Foo(id = null, someStringProperty= "someString")

Any idea how I can achieve that? It might look very hacky… but it would be really useful for the tests we have (and to convinde colleagues who love grrovy a bit more 😉 )

If you want people to use Kotlin to write tests, the best way would be to make it somehow possible to write Spock tests in Kotlin. 😄

well with kotest we do have a good alternative I think, it is more about the flexibility to test single fields of a data class now 🙂

You will need

kotlin-reflect

, but then you can use:

fun createFoo(propertyName: String, propertyValue: Any?): Foo {
    val primaryConstructor = Foo::class.primaryConstructor ?: error("Missing constructor")
    return primaryConstructor.callBy(
        mapOf(
            primaryConstructor.parameters.single { it.name == propertyName } to propertyValue
        )
    )
}

The propblem is, I want a test like this:

listOf(
          row("id", 5),
          row("someStringProperty", "someStringProperty")
      ).map { (field: String, value: Any) ->
        it("test $field=$value"){
val testdata = createFoo(field, value)
do something with it
}

So I basically want to automate tests without having to dulpicate anything. Would never think about it for production code of course, but for tests we do this regularly and it does make the tests very easy to read. and in groovy it is very easy as we mostly use Maps there. and I made the suggestion to move from spock/groovy tests to kotest/kotlin so I feel in the need of finding solutions that do not blow up the tests too much as they are already much different to spock 😉 Thanks for your help, this works like a charm 🙂

From a very quick look I wouldn't agree that kotest is anything near a good replacement for Spock. I see no integrated mocking and stubbing, and as far as I have seen you don't get the amazing assertion output that you get with Spock. To just name three of the most prominent points.

From my point of view, it is not AS GOOD AS spock, but I have the bit positive of using kotlin and for me/us it is a good enough alternative. I do find that with the kotest together with mockk you have a very nice set of assertions and the mocking also works well. I mean yes mockk is not integrated in kotest, but they do work well together in my opinion. But I guess people have different likes and dislikes so one person might think so and others different. All in all I can say that I started using JUnit 5 and I missed Spock like maaaad. But then I read about kotest and since then I do not miss it as much anymore. 🙂

I'm not sure that integrating a mocking libraries with a test framework is better than just using one of the several excellent choices of mocking libraries already available for Kotlin. The one killer feature of Spock that Kotest doesn't have is the power assert output. Other than that, I genuinely don't know why some people say Spock is better than Kotest.

I do not really understand what you mean by that. with kotest you doget that too I thought? What is missing here for you?

it("fail id"){
        Foo(1, "foo1") shouldBe Foo(2, "foo1")
      }

---

  it("fail name"){
        Foo(1, "foo1") shouldBe Foo(1, "foo2")
      }

Result

data class diff for Foo
Expected :Foo(id=2, name=foo1)
Actual   :Foo(id=1, name=foo1)
<Click to see difference>

org.opentest4j.AssertionFailedError: data class diff for Foo
└ id: expected:<2> but was:<1>

---

data class diff for Foo
Expected :Foo(id=1, name=foo2)
Actual   :Foo(id=1, name=foo1)
<Click to see difference>

org.opentest4j.AssertionFailedError: data class diff for Foo
└ name: expected:<"foo2"> but was:<"foo1">

Does it properly and nicely work for more complex expressions and things besides data classes like Spock does it? Spock shows you at each "dot" or operator in the expression what the state is and what does or does not match.

No that's not present in Kotest, which is the killer feature I mentioned was missing. @huehnerlady the power assertion feature of groovy is very very nice. It shows you the value at each level of an expression. So for

assert(x.y.z == a)

it will show you what x is, what y is on x, and what z is on y, so you can see where your expectation diverged.

"of Spock" 😉

I thought it was spock too, but it seems to be a groovy thing? http://www.groovy-lang.org/testing.html#_power_assertions

They copied it partly from Spock, but that's not what you get when using Spock

Ah ok

When using Spock, it's done by Spock

Got it

Disclaimer: In the meantime I became part of the Spock team 😄

Disclaimer: I'm part of the Kotest team 😂

That was obvious 😄

haha 🙂

nice for you to find each other, maybe you should have a chat? 😉 I do love spock and I agree that feature is great, to me it is essential to know what is wrong, I did not have any use cases yet where I was hoping for some more detailed information with the ‘common’ matchers. What I miss from spock is that you have a nice given/when/then/where structure, which unfortunately you have in kotest only with a very verbose set of functions (BehaviourSpec), but we found a spec that works for us alright and for the rest we miss I would start putting up issues as I find if you have a problem, ask for it, maybe contribute if you have time, but make yourself known. Having said that… IF spock would work for kotlin as well - AND with the same set of functionality as it does in groovy - I think I would be one of the first people to switch back (sorry @sam 🙈 )

lol that's ok, maybe I should use spock as well 😛

@huehnerlady "for kotlin" like writing in kotlin or testing kotlin code?

well the way kotest is developing I could imagine it could be a very good alternative to spock in future. So far it is a good-enough-for-me alternative 🙂

Yes, that would be amazing. But probably not happening unless someone very savvy in Kotlin Compiler Plugins and Groovy AST Transformations steps up to give it a shot. I'd also like being able to write Spock specs in Kotlin. Unfortunately I fear some things cannot work like omitting the data variables in the parameter list as then probably the compiler complains, unless the compiler plugin gets a chance to fix this up before the compiler complains.

I can understand that, what a shame. But hopefully kotest continues to blume 🙂