I am using Android Studio 3.0.1 and Kotlin 1.2.10 for my Android project.
When I run unit tests written in Kotlin (e.g. right click > Run), the Run Configuration that is created does not use the Android JUnit template. This means the project is built using the gradle assemble tasks instead of the compile tasks (used by the Android JUnit Run Configurations). This increases the build time significantly (~10x on my machine).
It seems that this behavior is controlled by the Kotlin plugin
See also Google Issue Tracker
Is there a way to use the Android Junit Run Configuration template as a default for Kotlin unit tests?