We built some of our test JDKs with configure option --enable-linkable-runtime, so no jmod dir is available.
ImageReaderTest does not take this nicely into account, it should be adjusted. Currently it fails with the following test output :

Test not run, NO jmods directory
org.opentest4j.TestSkippedException: Cannot create test helper (exploded image?)
at ImageReaderTest.getHelper(ImageReaderTest.java:220)
at ImageReaderTest.buildJImage(ImageReaderTest.java:176)
at ImageReaderTest.<init>(ImageReaderTest.java:77)
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:483)
at java.base/java.util.Optional.orElseGet(Optional.java:364)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1604)
JavaTest Message: JUnit Platform Failure(s): 1

[ JUnit Containers: found 6, started 4, succeeded 3, failed 1, aborted 0, skipped 0]
[ JUnit Tests: found 3, started 0, succeeded 0, failed 0, aborted 0, skipped 0]

java.lang.Exception: JUnit test failure
at com.sun.javatest.regtest.agent.JUnitRunner.runWithJUnitPlatform(JUnitRunner.java:179)
at com.sun.javatest.regtest.agent.JUnitRunner.main(JUnitRunner.java:110)
at com.sun.javatest.regtest.agent.JUnitRunner.main(JUnitRunner.java:76)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1474)

JavaTest Message: Test threw exception: java.lang.Exception: JUnit test failure
JavaTest Message: shutting down test