hello 👋 I have really weird error and I don't know how to fix. Can someone help me understand it? I don't have a function that long

Mockk is telling you that the reported call on HttpClient has not been stubbed. Probably in your test you created a mock of HttpClient and your code is calling it, even indirectly. If this is the case and you don’t need or bother stubbing that call you can declare a relaxed mock to avoid this:

val httpClient = mockk<HttpClient>(relaxed = true)

Yeah, I figured it out eventually. I can't mock extension methods, right?

actually you can https://mockk.io/#extension-functions