Testing DSL developed in Kotlin - unit-testing

Question

I'm working on a DSL using Kotlin, and I'm wondering about the best approach for testing it.
The top level element is an article, with a class, and a top level function for the DSL
class Article {
val children = mutableListOf<DocumentSection>()
}
inline fun article(init: Article.() -> Unit): Article {
val article = Article()
article.init()
return article
}
In the article I have a nested section.
class Section(val parent: Document, val title: String) {
val children = mutableListOf<Element>()
}
fun DocumentSection.text(text: String) = this.children.add(TextElement(this, text))
And an extension function to add a section to the article
inline fun Article.section(title: String, init: Section.() -> Unit): Section {
val section = Section(this, title)
section.init()
this.children.add(section)
return section
}
Testing the implementation
Now when testing the article, it is simple, but when testing nested items of the DSL, it becomes very verbose. And in this case I'm also relying on the article
class SectionDslTest : DescribeSpec() {
init {
describe("a section without content") {
val title = "section title"
val article = article {
section(title) {}
}
it("should have only the title set") {
article.children.first().title shouldBe title
}
}
}
}
In this case it would be best to just test section.title shouldBe title
The problem here of course are the extension functions. (Which are one of the best features of Kotlin, don't get me wrong).
I have also tested the Section class, which can be done just fine. But I believe that we should test what will be exposed to the user, and everything else can be a nice bonus, or it can even be bad if the extra tests are working agains you.
Anyway, here is the test on the Section class.
class SectionTest : DescribeSpec() {
init {
describe("a document section with some text") {
val parent = Article()
val title = "section title"
val section = Section(parent, title)
it("should have the parent article set") {
section.parent shouldBe parent
}
it("should have the title set") {
section.title shouldBe title
}
}
}
}
What's the best approach to test this?