UPD 1:By testcases here I mean pretests only listed on problems’ page(usually helpful for short contests)
In Codechef, hardly - they don’t publish test cases. Codeforces only shows a reasonably small part of the test cases, so it’s possible only to a limited extent. You can’t make a plugin get something that the site itself does not provide
Ok, so you mean the samples. I think copy-pasting is the simplest option… and the best with regards to preparation for contests that don’t allow haxxed tools of various kinds.
You can install CHelper for IntelliJ IDEA (for JAVA only). It works for Codeforces and Codechef as well. There is no plugin available till now. I am planning to build one as the source code of similar plugins is available on github. Try the Eclipse Coder plugin for TopCoder. For more discussion on the same topic, there is already an existing question here. So please continue the discussion there.
Alright, but that was still unanswered so it will be better to continue the discussion at that thread only. I’ll modify it to ask the particular question.