Dorer

Dorer is a library for property based testing.

It helps you explore different execution paths and inputs with your property based tests.

Examples

This property tests a function named biggest, which should return the biggest element in a nonempty list. We check that the result is always equal to the last element in the sorted list:

simple_test(_Config) ->
  dorer:check(fun() ->
    List = dorer:gen(dorer_generators:list(dorer_generators:integer())),
    case List of
      [] -> ok;
      _ ->
        ?assertEqual(lists:last(lists:sort(List)), biggest(List))
    end
  end).

If biggest is implemented incorrectly and always returns the first element in a list, Dorer finds the following counter example.

Generated Values:
 [default]: {list,[integer]} => [-1,0]


LOG:

ERROR error: {assertEqual,[{module,dorer_examples_SUITE},
                           {line,22},
                           {expression,"biggest ( List )"},
                           {expected,0},
                           {value,-1}]}

Usage

Add dorer to your list of dependencies. Then use dorer:check to run a function multiple times, each exploring a different execution. This can be done from within a normal common test suite or eunit test (if you set the timeout high enough).

Inside the check function you should call dorer:gen to generate different values. For debugging use dorer:log.

Options

Options are specified using a map that can have the following entries:

-type strategy() :: small | random.
-type options() :: #{
    strategy => strategy(),
    max_shrink_time => {pos_integer(), erlang:time_unit()},
    n => integer(),
    print_generated_values => boolean() | if_log_empty
}.

Default values:

#{
  strategy => random,
  max_shrink_time => {3, second},
  n => 100
  print_generated_values => if_log_empty
}

Build

$ rebar3 compile