In CDS/AOT testing, we have a lot of code that deal with compiling/packaging modules, as well as running various child processes for the training/assembly/production phases.

Currently, these operations are done in many low-level steps, so it's difficult to understand and maintain:

https://github.com/openjdk/jdk/blob/fcc2a24291d499f7149debad1250903ddc369d91/test/hotspot/jtreg/runtime/cds/appcds/jigsaw/modulepath/ExportModule.java

=============================
Proposal:

For simplification, the following APIs should be added (examples)

======= build two modular JAR files into <modulePath>
    CDSModulePackager modulePackager = new CDSModulePackager(SRC);
    modulePath = modulePackager.getOutputDir().toString();

    modulePackager.createModularJar("com.foos");
    modulePackager.createModularJar("com.needsfoosaddexport",
                                    "--add-exports",
                                    "com.foos/com.foos.internal=com.needsfoosaddexport");

============= running training/assembly/production phases
    SimpleCDSAppTester.of("moduleNeedsJdkAddExport")
       .classpath(dummyJar)
       .modulepath(modulePath)
       .addVmArgs("--add-modules", "com.needsjdkaddexport",
                  "--add-exports", "java.base/jdk.internal.misc=com.needsjdkaddexport", "-Xlog:cds")
       .appCommandLine("-m", "com.needsjdkaddexport/com.needsjdkaddexport.Main")
       .setAssemblyChecker((OutputAnalyzer out) -> {
              out.shouldContain("Full module graph = enabled");
           })
       .setProductionChecker((OutputAnalyzer out) -> {
               out.shouldContain("use_full_module_graph = true; java.base");
           })
       .runStaticWorkflow()
       .runAOTWorkflow();