Consider a jtreg test that throws some exception. If getMessage (or perhaps toString) on this exception returns a string containing a newline, this will corrupt the output in JTreport/text/summary.txt.

Well, "corrupt" is rather a strong word, but various downstream tools (such as the makefiles) expect the summary.txt file to have a single line per test in the suite, along with a status ("Passed", "Failed", "Not run") plus additional messages. If these additional messages have newlines, it will violate the one-line-per-test assumption, counts will be thrown off, etc.

Here's a simple example:

/*
 * @test
 * @run main Test1
 */
public class Test1 {
    public static void main(String[] args) throws Exception {
        throw new Error(String.format("foo%nbar"));
    }
}


A slightly more complicated example has the following as the body of main():

        throw new java.rmi.RemoteException("outer", new Exception("inner"));

In this case the getMessage method of RemoteException puts a newline into its output, in order to separate the outer exception's message from the inner exception's message.

It's probably reasonable for jtreg to scrub such messages and to do something like replacing newlines with spaces.