java.lang.IllegalStateException: Could not find sun.misc.Unsafe while @MockK

Just to follow the answer from @lukaszrys I had this exact problem with running Mockito under Java 11. I was using Gradle and adding the following to my dependencies fixed it for me:

testCompile "net.bytebuddy:byte-buddy:1.8.22"
testCompile "net.bytebuddy:byte-buddy-agent:1.8.22"