Running the sigtest tool to test the signatures in a library jar file fails to find the classes in the jar file if -static is not used. For example:

${JAVA_HOME}/bin/java --add-modules java.se.ee \
        -jar sigtest.jar test \
        -classpath sigtest.jar:javax.mail.jar \
        -Package javax.mail \
        -FileName tests/javax.mail_1.6_java_9.sig

Produces this output:

SignatureTest report
Base version:
Tested version:
Check mode: src [throws normalized]
Constant checking: on


Missing Classes
---------------

javax.mail.Address
javax.mail.AuthenticationFailedException
...

The attached zip file reproduces the problem.