JDK-8253119, in Java 18, removed support for the jdk.net.usePlainSocketImpl property. Since then, it no longer has any special meaning. The test/jdk/sun/security/ssl/SSLSocketImpl/SSLSocketReset.java was introduced in JDK-8268965 and sets this system property to true. The test itself was introduced to exercise PlainSocketImpl, but it doesn't have any PlainSocketImpl related internal implementation details, so I think it's OK to retain the test and just remove the reference to the obsolete property.