The code in:
test/langtools/tools/javac/jvm/ClassRefDupInConstantPoolTest.java
attempts to read class-file bytes from the compiled test JAR via:

----
ClassModel cls = ClassFile.of().parse(
    ClassRefDupInConstantPoolTest.class
        .getResourceAsStream("ClassRefDupInConstantPoolTest$Duplicates.class")
        .readAllBytes());
----

where the `Duplicates` class is just defined as code in the test file:

----
    class Duplicates {
        String concat(String s1, String s2) {
            return s1 + (s2 == s1 ? " " : s2);
        }
    }
----

This works when run from "make test", but fails when run from IntelliJ via the JTreg plugin with:

----
java.lang.NullPointerException: Cannot invoke "java.io.InputStream.readAllBytes()" because the return value of "java.lang.Class.getResourceAsStream(String)" is null
at ClassRefDupInConstantPoolTest.main(ClassRefDupInConstantPoolTest.java:40)
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.NullPointerException: Cannot invoke "java.io.InputStream.readAllBytes()" because the return value of "java.lang.Class.getResourceAsStream(String)" is null
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.NullPointerException: Cannot invoke "java.io.InputStream.readAllBytes()" because the return value of "java.lang.Class.getResourceAsStream(String)" is null
----

This test might be a symptom of a pattern which generally won't work in IntelliJ, but it can be easily changed to use the toolbox to compile on-the-fly.