I'm a bit surprised by this given that IBM is a long time license holder and I can remember JavaOne keynotes where Oracle celebrated IBM "joining" OpenJDK.
> Java Compatibility Kit (JCK) / TCK Compliance
> At this stage the London Jamocha Community CIC (aka LJC) has not been able to reach an agreement with Oracle to use the Java SE Technology Compatibility Kit (TCK) under the terms of the OpenJDK Community TCK License Agreement (OCTLA).
> We will continue to work with Oracle on this matter.
> All AdoptOpenJDK binaries are tested with our suite of functional, integration, stress, and performance tests, including real workloads from popular languages and applications. We are very confident in the quality of our builds.