MettleCI is built and tested using the Adoptium JDK (the project and brand name for the OpenJDK-compatible binaries produced by the Eclipse Foundation). MettleCI isn’t tested against other OpenJDK distributions as this would be impractical, given the number of them and the breadth of testing that would have to be performed for every MettleCI component.
One of the key test suites used to legitimise a branded OpenJDK distribution is the Java Compatibility Kit (JCK), distributed to signatories to the OpenJDK Community TCK License Agreement (OCTLA). The Eclipse Foundation and many JDK distributors has signed that agreement and use the JCK. When determining whether or you your preferred JDK distribution is compatible with MettleCI you should look for a statement by the distributor that your JDK is certified against the OpenJDK Java Compatibility Kit for Java SE 8. Take a look, as an example, at this release announcement for the ‘Azul’ Java 1.8 runtime that states this unambiguously.