Unit Test fails with GrailsConfigurationException - cannot find responsible line of code

I am writing unit tests for my Grails 3.0.3 application with standard spock framework. Everything as scaffolded by

grails create-app  

I created my unit test with

grails create-unit-test

Added manually @TestFor annotation and test logics. I get

mypackage.MyClassSpec > test myMethod method FAILED
org.grails.core.exceptions.GrailsConfigurationException

GIST of My test class (generalized and simplified)

There is no line number in stacktrace after running

grails test-app --stacktrace

How can I find out what is causing this exception?