[JENKINS-24399] A test to reproduce JENKINS-24399

[ikedam]

This is a demonstration for JENKINS-24399 Modifying files in class directories can bypass approval in script-security (or class directories are accepted as classpaths).
Do not merge.

script-security 1.5 allows to use a class directory as an additional classpath.
This test shows that users can use class directories whose contents are modified without administrators' approval.

[cloudbees-pull-request-builder]

plugins » script-security-plugin #65 UNSTABLE
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[ikedam]

testClasspathWithClassDirectory fails as the build succeeds even after modified the contents of class directory.
When the library is modified after approval, the build using that library should fail without new approval.