When the output for a test gets too big, JT Harness "truncates" the middle of the output and does a reasonably good job of leaving a big marker where it has done so.

But even so, it can be easy to miss if you are not looking for it -- e.g. if you are using grep to detect for expected text.

Maybe there's a way to additionally mark the file in any even more obvious way. For example, append "(WARNING: OUTPUT TRUNCATED)" to the final status message, which is probably the first thing anyone encounters when they have to investigate a failure.