There are a few SuppressWarnings statements in the test lib that could be cleaned up.

Furthermore, in jdk/test/lib/process/StreamPumper.java, the printing of IOException stack traces when the input stream is simply closed causes quite some noise, e.g. dozens of
java.io.IOException: Stream closed
at java.base/java.io.BufferedInputStream.getBufIfOpen(BufferedInputStream.java:169)
at java.base/java.io.BufferedInputStream.read(BufferedInputStream.java:335)
at java.base/java.io.BufferedInputStream.fill(BufferedInputStream.java:245)
at java.base/java.io.BufferedInputStream.read1(BufferedInputStream.java:285)
at java.base/java.io.BufferedInputStream.read(BufferedInputStream.java:344)
at java.base/java.io.FilterInputStream.read(FilterInputStream.java:107)
at jdk.test.lib.process.StreamPumper.run(StreamPumper.java:109)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:830)
in sun/tools/jcmd/TestProcessHelper which don't help.