when I can just use trivial methods from standard library:

And also, in my opinion, this is a very weak argument. Why bother using Kotlin if you can write things trivially in Java? Why bother using Java if you can write things trivially in C?

Re:

Why bother using Kotlin if you can write things trivially in Java?

because I am several times more productive with Kotlin. A smallish effort to learn it pays off in a few days. With

"substring".shouldContain("str")

I am just as productive as with

assertTrue("substring".contains("str"))

and I've spent/wasted some time to learn it. Not worth it, for trivial cases at least.

just as productive as with

Perhaps when writing 10 assertions. Reading them again after some time is what really bites you

yes

withClue("Name should be present") { user.name shouldNotBe null }

is clearly much shorter than `assertTrue(user.name.isNotNull(), "Name should be present") `` of course kotest might have lots of advantages, but is it really terse?