14 January 2009

Announcing FsCheck 0.4

It's been a month and a half since the last release of FsCheck. Time for an update!

Major changes:

  • Rewrote the back end using typeclasses. The result: much less reflection, cleaner code, and improved flexibility in the property combinators. In particular, the 'prop' and 'propl' combinators can now be omitted. Properties can take any nunber of arguments, that do not need to be tupled. Generators can now be more easily defined, and function generators are also derived based on type.
  • Two major new features were contributed generously by Howard Mansell and team at Credit Suisse. Most of the implementation was done by Neil Mitchell, who has also helped me a lot in integrating the changes in the main FsCheck branch. Thank you both!
    The features are:
    • Automatic generation of records, discriminated unions (including recursive ones), arrays and tuples. So once you define a generator for a type, FsCheck can now automatically generate lists, arrays, record types, functions, discriminated unions and options involving that type.
    • Shrinking. Especially with recursive datatypes, counter examples can become quite large. FsCheck now automatically shrinks these examples to a smaller one, making bug finding lots easier.

Minor changes:

  • Some performance improvements
  • Improvements in FsCheck's output.
  • Factored out the function that prints the result of a test, so you can use it in your IRunner implementation if necessary
  • Because FsCheck uses less reflection, stack traces of exceptions when a test case fails are shorter and clearer

Breaking changes:

  • quickCheck no longer checks types; instead use quickCheckAll, verboseCheckAll or checkAll. quickCheck is the preferred way to check properties: it is faster, clearer and more flexible.
  • You'll need to redefine some of your custom generators; the mechanism to define and register generators has changed. See the manual for details, an don't hesitate to ask questions.

This is a bit of an intermediary release - for v0.5 I'd like to integrate shrinking better, so you can define your own shrinkers for a given datatype. Should be straightforward now that I've reworked the back-end, but I wanted to get this release out first - I think shrinking and the reflective datatype generators by themselves are worth a new release. Most of the churn should be over now, I'm finally happy now with the way a user can define new properties and generators.


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