Add a withData() overload that accepts one element

[Virtlink]

In the process of writing tests, I spent half an hour messing with types and type signatures trying to figure out why the following test gave me type errors:

import io.kotest.core.spec.style.FunSpec
import io.kotest.datatest.withData

class Tests: FunSpec({
    withData(
        Triple("a", 2, "aa"),
    ) { (input, count, expected) ->
        // ... //
    }
})

It gave me two errors. On (input, count, expected) I got:

Cannot infer a type for this parameter. Please specify it explicitly.
value-parameter `<name for destructuring parameter 0>`: [Error type: Cannot infer a lambda parameter type]

And on withData I got:

None of the following functions can be called with the arguments supplied.
RootScope.withData(Collection<TypeVariable(T)>, suspend ContainerScope.(TypeVariable(T)) → Unit)   where T = TypeVariable(T) for    fun <T> RootScope.withData(ts: Collection<T>, test: suspend ContainerScope.(T) → Unit): Unit defined in io.kotest.datatest
RootScope.withData(Map<String, TypeVariable(T)>, suspend ContainerScope.(TypeVariable(T)) → Unit)   where T = TypeVariable(T) for    fun <T> RootScope.withData(data: Map<String, T>, test: suspend ContainerScope.(T) → Unit): Unit defined in io.kotest.datatest
RootScope.withData(Sequence<TypeVariable(T)>, suspend ContainerScope.(TypeVariable(T)) → Unit)   where T = TypeVariable(T) for    fun <T> RootScope.withData(ts: Sequence<T>, test: suspend ContainerScope.(T) → Unit): Unit defined in io.kotest.datatest

Of course, maybe its obvious to you, dear reader, but it was not at all obvious to me what the issue was: there is no overload of withData() that accepts one element. You have to specify a minimum of two tests to withData(). And the error messages led me astray. So therefore my feature request:

Could you add an overload to withData() that accepts one element?

[kshired]

You can write a test use list as follows.

import io.kotest.core.spec.style.FunSpec
import io.kotest.datatest.withData

class Tests: FunSpec({
    withData(
        listOf(Triple("a", 2, "aa"))
    ) { (input, count, expected) ->
        // ... //
    }
})

[Virtlink]

Thank you, that is a good workaround once one is aware of the issue when using one element. My main issue is that I found it unexpected (and unintuitive and undocumented) that the vararg-overload of withData expects at least two elements. So I propose to add an overload that accepts one element:

fun <T> RootScope.withData(first: T, test: suspend ContainerScope.(T) -> Unit) =
    withData(listOf(first), test)

fun <T> RootScope.withData(nameFn: (T) -> String, first: T, test: suspend ContainerScope.(T) -> Unit) =
    withData(nameFn, listOf(first), test)

[kshired]

@Virtlink

There's some reason why we cannot add overloaded function that accept only one element.

kotest/kotest-framework/kotest-framework-datatest/src/commonMain/kotlin/io/kotest/datatest/container.kt

Line 18 in cd60ed6

) = // we need first and second to help the compiler disambiguate

[sksamuel]

Broken on the following issue in kotlin:
https://youtrack.jetbrains.com/issue/KT-66470/False-overload-resolution-ambiguity-when-both-vararg-and-collection-match-with-a-trailing-function-with-a-parameter