What have you found for these years?

2014-01-24

Think about a talk for rubyconf.tw/2014

Doh, I believe this description is far too long though...
Still thinking.

RubyQC -- A conceptual QuickCheck library for Ruby.

How do we make sure our programs work as expected?
Taking it to the extreme, of course we prove it formally.
We have Agda for Haskell people, or Coq for OCaml people.

However, in most cases we don't really care if they are
100% correct. Do we care PRNGs are really random
in games? Some people might care, we don't. Can we
prove halting problem? Of course not, but we do need
termination check at times.

For most cases, an army of tests is far good enough.
Usually we write scenario based tests. We first assume
things, and then do things, finally verify results. This is
quite simple, but cannot really cover most of the inputs
without great effort.

QuickCheck took another approach. Instead of writing
scenario, we think about what properties do our programs,
or functions have, giving a range of inputs. Suppose
we want to test the reverse function, instead of testing
against a fixed set of lists and verify a fixed set of results,
we think about what properties does reverse have.

For example, if we reverse and reverse a list, the result
should be equal to the original list. With QuickCheck, it
could then generate arbitrary random lists to the property
function you just wrote, and verify if the property holds.
By default, it would generate 100 test cases.

This approach would force you think more about the
precondition and postcondition, eliminating unusual
corner cases you might never think of, and force you
think what are the functions we're really writing. We
could also raise the number of test cases by configuring
it and raise our level of confidence about correctness.

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