Improve Kotlin integration testing documentation

Closes gh-22875

Author: sdeleuze

src/docs/asciidoc/languages/kotlin.adoc

@@ -794,6 +794,9 @@ This section addresses testing with the combination of Kotlin and Spring Framewo
 The recommended testing framework is https://junit.org/junit5/[JUnit 5], as well as
 https://mockk.io/[Mockk] for mocking.
 
+NOTE: If you are using Spring Boot, see
+https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-kotlin-testing[this related documentation].
+
 ==== Constructor injection
 
 As described in the <<testing#testcontext-junit-jupiter-di#spring-web-reactive, dedicated section>>,

src/docs/asciidoc/testing.adoc

@@ -6101,3 +6101,5 @@ See the following resources for more information about testing:
   Maven) that is targeted at database-driven projects and, among other things, puts your
   database into a known state between test runs.
 * https://sourceforge.net/projects/grinder/[The Grinder]: Java load testing framework.
+* https://github.com/Ninja-Squad/springmockk[SpringMockK]: Support for Spring Boot
+  integration tests written in Kotlin using https://mockk.io/[MockK] instead of Mockito.