I totally disagree that Unit Test writing is something that “all” developers hate. On the contrary, most of those I know love it.
There is nothing more satisfying than developing software in the TDD, which then, after several hours or even days, first enters a test environment and runs (almost) without errors. And all thanks to the tests!
I miss an indication of the used Kotlin stdlib version. Testing with the default stdlib (jdk 6 level) against Java 11 would be pretty unfair. The stdlib-jdk8 should perform much better under Java 11.
But still a very elaborate article. Good work :-)