I've not tried an automated system like you describe but I have tried to make
test scripts available that compare the output of their programs to correct
output. That way the students can check their progress as they work. In
general, I find this approach doesn't work well for grading because in order to
specify a homework to the point where the students' output matches your output,
the homework ends up being 10 pages long (not unlike a legal document).
For example, in a number of instances I'd say "the function should return a
number..." and then I'd compare the returned result to the actual answer. But a
student would 'print' the number instead, not knowing the difference between
'return+autoprint' and 'print'. I found it difficult to write a test script
that gives partial credit for getting the answer right but the concept wrong.
Perhaps that's a problem with the way I grade things, but I found it difficult
to write an acceptable test script.
-roger
Barry Rowlingson wrote:
Someone recently suggested building a system for automatically testing
student's R programs. They would upload them to our Virtual Learning
Environment, which would then run the code on some inputs and see if
it got the right output. If it does, the student scores points for
that course.
My first thought was "you want to run unchecked, student-submitted
code on a server that has access to students' grades?".
Can this be done securely? The idea might be to run R in a
chroot-jail, freshly generated for each run. The jail would not be
able to access anything outside of it, and once the R session has
finished the calling process can pick up the output from within the
jail.
Maybe that's overkill. Perhaps if you run the user's code as an
ordinary user and store the answers/results in a directory only root
can read that would work (given no local root exploits). Other
precautions could include limiting the runtime or cputime for the R
session. It might be necessary to limit network access too.
Anyone done anything like this? Personally I think there are too many
other problems with automated systems like this, particularly that
just because a program produces the correct output that makes it a
good one. Sure, at the production stage that's a requirement, but I'd
rather students learnt to program well than to program correctly -
since correctness follows goodness but goodness does not follow
correctness. But that's an argument for another day!
Barry
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