You have to mock whatever is inside the inline call

Oh dear. There is a lot of code in that function... And it's the code inside that I want to test.

What do you mean?

I have to say, this is beyond me. Kotlin encourages all these inline functions and lambdas, but testing code which uses them hurts my brain.

I suspect that perhaps you're misusing lambdas and inline functions

All I want to do is mock my way around reading a directory of files...

project.dirs.sources.walk().forEachIndexed { index, mdFile ->
	val inputStream = mdFile.inputStream()
	val document = parseMarkdown(inputStream)
}

In this cases I usually have that reading in a class or function, such as

readInputStream(file)

OK, I've got a lot to learn it seems. Kotlin makes it very easy to just through yourself in, but working alone also means it's easy to pick up bad habits.