JesTer

JesTer finds code that is not covered by tests. JesTer makes some change to your code, runs your tests, and if the tests pass JesTer displays a message saying what it changed.

JesTer is different than CodeCoverageTools, because it can find code that is executed by the running of tests but not actually tested. However, JesTer is not meant as a replacement for CodeCoverageTools, merely as a complementary approach.

JesTer is for Java code and JUnit tests. Now there is also PesTer (also available from http://sourceforge.net/projects/jester/), for Python code and PyUnit tests.

(JesTer is one of the free MutationTestingTools)

--IvanM

download from: http://sourceforge.net/projects/jester/

home page http://www.jesterinfo.co.uk

a paper on JesTer was presented at XP2001: http://www.xp2003.org/conference/papers/Chapter20-Moore.pdf

A posting about how JesTer helped find a simplification in some code from an article on test first programming: http://groups.yahoo.com/group/extremeprogramming/message/32277

I found a short article mentioning JesTer: http://radio.weblogs.com/0109827/2002/09/15.html

There is another Java Testing thing called Jester which is completely different (I haven't yet tried it): http://smile.jcon.org/soft/product/jester/Jester.html

change log is on SourceForge (http://sourceforge.net/projects/jester) - now has a timeout on running tests so it can handle mutations that cause infinite loops.

Example of results from running JesTer: http://jester.sourceforge.net/jester/acceptancetests/Untested.html

JesterDiscussion JesterFAQ JesterAcknowledgements JesterBugs

JesterStories (put your feature requests here)

When Ivan first told us about his idea for a test-tester I was not convinced of the utility of such a thing. However, having had a play around with the thing I'm quite impressed. Finding a branch of the JUnit Money example that was untested, then devising a test for that branch was fun.

It seems as if JesTer would be more useful than a regular profiler. A profiler, to my mind, indicates code to take out (becuase the test suite doesn't require it to pass). JesTer gives more useful information because it provokes you to examine the code more closely, the information about what could be changed and still pass the current tests gives a useful new way to think about what the code says. --KeithB

I'm now convinced that Jester and its ilk (wherever they are) go to the heart of what unit testing means in XP. See http://c2.com/cgi/wiki?UnitInUnitTestIsntTheUnitYouAreThinkingOf -- KeithB

Coincidentally, I came across someone at DrKB who was keen on something called "mutation testing". Seemed exactly like what Jester does. --PaulS