# ct_property_test

###
Module

ct_property_test

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Module Summary

Support in Common Test for running property-based tests.

###
Since

Module ct_property_test was introduced in OTP 17.3.

###
Description

This module helps running property-based tests in the Common Test framework. One (or more) of the property testing tools

- QuickCheck,
- PropEr or
- Triq

is assumed to be installed.

The idea with this module is to have a Common Test test suite calling a property testing tool with special property test suites as defined by that tool. The tests are collected in the test directory of the application. The test directory has a subdirectory property_test, where everything needed for the property tests are collected. The usual Erlang application directory structure is assumed.

A typical Common Test test suite using ct_property_test is organized as follows:

    -module(my_prop_test_SUITE).
    -compile(export_all).

    -include_lib("common_test/include/ct.hrl").

     all() -> [prop_ftp_case].

     init_per_suite(Config) ->
         ct_property_test:init_per_suite(Config).

     %%%---- test case
     prop_ftp_case(Config) ->
         ct_property_test:quickcheck(
           ftp_simple_client_server:prop_ftp(),
           Config
          ).

and the the property test module (in this example ftp_simple_client_server.erl) as almost a usual property testing module (More examples are in the User's Guide):

    -module(ftp_simple_client_server).
    -export([prop_ftp/0...]).

    -include_lib("common_test/include/ct_property_test.hrl").

    prop_ftp() ->
        ?FORALL( ....

###
Exports

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init_per_suite(Config) -> Config | {skip, Reason}
OTP 17.3

Initializes and extends Config for property based testing.

This function investigates if support is available for either QuickCheck, PropEr or Triq and compiles the properties with the first tool found. It is supposed to be called in the init_per_suite/1 function in a CommonTest test suite.

Which tools to check for, and in which order could be set with the option {prop_tools, list(eqc|proper|triq)} in the CommonTest configuration Config. The default value is [eqc, proper, triq] with eqc being the first one searched for.

If no support is found for any tool, this function returns {skip, Explanation}.

If support is found, the option {property_test_tool,ToolModule} with the selected tool main module name (eqc, proper or triq) is added to the list Config which then is returned.

The property tests are assumed to be in a subdirectory named property_test. All found Erlang files in that directory are compiled with one of the macros 'EQC', 'PROPER' or 'TRIQ' set, depending on which tool that is first found. This could make parts of the Erlang property tests code to be included or excluded with the macro directives -ifdef(Macro). or -ifndef(Macro)..

The file(s) in the property_test subdirectory could, or should, include the ct_property_test include file:

    -include_lib("common_test/include/ct_property_test.hrl").

This included file will:

- Include the correct tool's include file
- Set the macro 'MOD_eqc' to the correct module name for the selected tool. That is, the macro 'MOD_eqc' is set to either eqc, proper or triq.

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quickcheck(Property, Config) -> true | {fail, Reason}
OTP 17.3

Calls the selected tool's function for running the Property. It is usually and by historical reasons called quickcheck, and that is why that name is used in this module (ct_property_test).

The result is returned in a form suitable for Common Test test suites.

This function is intended to be called in test cases in test suites.

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present_result(Module, Cmds, Triple, Config) -> Result
OTP 22.3

Same as present_result(Module, Cmds, Triple, Config, [])

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present_result(Module, Cmds, Triple, Config, Options) -> Result
OTP 22.3

### Types

Module = module()
Cmds =
the list of commands generated by the property testing tool, for example by proper:commands/1 or by proper:parallel_commands/1
Triple =
the output from for example proper:run_commands/2 or proper:run_parallel_commands/2
Config =
the Common Test Config in test cases.
Options = [present_option()]
present_option() = {print_fun, fun(Format,Args)}
| {spec, StatisticsSpec}
The print_fun defines which function to do the actual printout. The default is ct:log/2. The spec defines what statistics are to be printed
Result = boolean()
Is false if the test failed and is true if the test passed

Presents the result of stateful (statem) property testing using the aggregate function in PropEr, QuickCheck or other similar property testing tool.

It is assumed to be called inside the property called by quickcheck/2:

    ...
    RunResult = run_parallel_commands(?MODULE, Cmds),
    ct_property_test:present_result(?MODULE, Cmds, RunResult, Config)
    ...

See the User's Guide for an example of the usage and of the default printout.

The StatisticsSpec is a list of the tuples:

- {Title::string(), CollectFun::fun/1}
- {Title::string(), FrequencyFun::/0, CollectFun::fun/1}

Each tuple will produce one table in the order of their places in the list.

- Title will be the title of one result table
- CollectFun is called with one argument: the Cmds. It should return a list of the values to be counted. The following pre-defined functions exist:
  - ct_property_test:cmnd_names/1 returns a list of commands (function calls) generated in the Cmnd sequence, without Module, Arguments and other details.
  - ct_property_test:num_calls/1 returns a list of the length of commands lists
  - ct_property_test:sequential_parallel/1 returns a list with information about sequential and parallel parts from Tool:parallel_commands/1,2
- FrequencyFun/0 returns a fun/1 which is supposed to take a list of items as input, and return an iolist wich will be printed as the table. Per default, the number of each item is counted and the percentage is printed for each. The list [a,b,a,a,c] could for example return

       ["a 60%\n","b 20%\n","c 20%\n"]

  which will be printed by the print_fun. The default print_fun will print it as:

       a 60%
       b 20%
       c 20%

The default StatisticsSpec is:

- For sequential commands:

      [{"Function calls", fun cmnd_names/1},
       {"Length of command sequences", fun print_frequency_ranges/0,
                                                        fun num_calls/1}]

- For parallel commands:

      [{"Distribution sequential/parallel", fun sequential_parallel/1},
       {"Function calls", fun cmnd_names/1},
       {"Length of command sequences", fun print_frequency_ranges/0,
                                                        fun num_calls/1}]