This currently manifests if you run Zero with compiler/codecache/cli tests (part of tier1):

$ CONF=linux-x86_64-zero-fastdebug make exploded-test TEST=compiler/codecache/cli/

STDERR:
java.lang.RuntimeException: Unknown VM mode.
at jdk.test.lib.cli.CommandLineOptionTest.getVMTypeOption(CommandLineOptionTest.java:504)
at jdk.test.lib.cli.CommandLineOptionTest.verifyOptionValueForSameVM(CommandLineOptionTest.java:397)
at compiler.codecache.cli.codeheapsize.GenericCodeHeapSizeRunner.run(GenericCodeHeapSizeRunner.java:42)
at compiler.codecache.cli.common.CodeCacheCLITestCase.run(CodeCacheCLITestCase.java:62)
at compiler.codecache.cli.common.CodeCacheCLITestBase.runTestCases(CodeCacheCLITestBase.java:58)
at compiler.codecache.cli.codeheapsize.TestCodeHeapSizeOptions.main(TestCodeHeapSizeOptions.java:86)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:312)
at java.base/java.lang.Thread.run(Thread.java:833)

While these tests are compiler tests, and they should arguably never run with Zero, the problem is in shared code, which can be used in future by other non-compiler tests.