January 2019
Intermediate to advanced
376 pages
8h 49m
English
?SHRINK is conceptually the simplest of the two macros that can be used to impact shrinking. It is best used to pick a custom zero point toward which PropEr will try to shrink data. You can do this mainly by giving the framework a normal generator for normal cases, and then suggesting it uses other simpler generators whenever an error is discovered.
The macro takes the form ?SHRINK(DefaultGenerator, [AlternativeGenerators]) in Erlang, and shrink(default_generator, [alternative_generators]) in Elixir. The DefaultGenerator will be used for all passing tests. Once a property fails, however, ?SHRINK lets us tell PropEr that any of the alternative generators in the list are interesting ways to get simpler relevant data. ...