The test seems to fail because the "gen-separate" directory is not empty:

test vm.InterfaceAccessFlagsTest.testPrivateMethodCall(): failure
java.lang.RuntimeException: java.nio.file.DirectoryNotEmptyException: .\\gen-separate\\1
at separate.Compiler.deleteDir(Compiler.java:237)
at separate.Compiler.lambda$cleanup$1(Compiler.java:243)
at java.util.ArrayList.forEach(ArrayList.java:1297)
at separate.Compiler.cleanup(Compiler.java:243)
at vm.InterfaceAccessFlagsTest.testMethodCallWithFlag(InterfaceAccessFlagsTest.java:70)
at vm.InterfaceAccessFlagsTest.testPrivateMethodCall(InterfaceAccessFlagsTest.java:76)