Quickcheck 0.6 Release

The version 0.6 of Quickcheck is ready to use. The main features are support for deterministic execution of generators and improvements on generators. The JUnit runner support was removed in this release.

You can read an in detail description of deterministic execution in this blog post.

The 0.6 release adds the following generators:
  - map generator maps(Generator<K> keys, Generator<V> values)
  - subset generator sets(Set<T>)
  - submap generator maps(Map<K, V>)
  - unique generator using a Comparator<T> to decide if two values are considered equivalent: uniqueValues(Generator<T>, Comparator<? super T>)
  - excluding generator based on a collection of input and a collection of excluded values: excludeValues(Collection<T> values, Collection<T> excluded
  - content generator type parameter are now co-variant for lists, iterators, sets and object arrays to allow creation of super type container generators (like Generator<List<Object>> = lists(integers()))
- PrimitiveGenerator added generators:
  - generator for java.lang.Object instances

The dropped Junit Runner support means that the @ForAll annotation is no longer supported. Until lambda expression are supported  in Java (hopefully) the Iterable adapter is a good workaround that allows to execute tests without too much boiler-plate. If you need all features the inner class will work just fine. Inner classes will become much better with the SAM-type conversion in Java 8 which is part of the language changes in Project Lambda.

The general development direction and the main theme I’ve been working on besides the release was the support for generator expressions. This is a good way to implement tests for equals methods where a equals method should return false when one of the significant attributes of an object is not equal. You have to write a lot of boiler-plate to test a simple statement like: “This is not equal if one of the attributes is not equal” now. With generator expression this should become much easier.

It’s quite tricky to create a nice API for expressions. One cul-de-sac was to implement it as a builder with a fluent interface. The method chaining is not an adequate. The chaining forces you to linerialize the definition of the expression. This does not fit well into the world of generators where delegation and nesting are natural concepts. I burned some time before I got that the underlying problem cannot be fixed with a clever API.  I hope the current approach terminates and the expression support is something you can work with in the 0.7 release.

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