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If no value has been specified when the build is initiated, a directory unique to the current operating system user will be created and used within the JVM's temporary directory as advertised by the java.io.tmpdir system property. This directory is not deleted by the runner after the test build.

answered my own question from the docs...i don't know why the default behavior is to not delete it/cleanup. and there seems to be no sane mechanism to tell it to do so automatically, which is disappointing

IIRC It's an optimization to make it so you don't need to reinstall Gradle versions again and again between test runs

Aah, that makes sense to me now, thank you for the explanation