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Proposition

Lightweight property-based testing library for PHP. Inspired by Python's Hypothesis library.

Installation

Because the API is not fully stable yet, you must specify dev-master to composer install:

composer install jonathrg/proposition:dev-master

What is property-based testing?

According to the first blog post I found about it,

Property-based tests make statements about the output of your code based on the input, and these statements are verified for many different possible inputs. A property-based testing framework runs the same test over and over with generated input.

This is in contrast to example-based testing, where you have to hand-write your inputs. A property-based testing library like Proposition lets you test your code with thousands and thousands of input combinations (including all sorts of edge cases) with just a few lines of code. As an example, Proposition uses itself to test itself, and does so with about 4000 assertions per line of test code.

Documentation

See the Wiki, especially the Quick reference

Example usage

There are some examples of the values Proposition generates in the examples folder. Run them with PHP from the command line (see the readme.md there)

Here's a toy example showing how you would use Proposition to check whether your awesome reimplementation of abs($a) == abs($b) actually works.

use Proposition/Proposition;

function equal_magnitude($a, $b)
{
    return ($a = $b) || ($a == -$b);
}

$proposition = new Proposition();

$proposition
    ->given(Proposition::integers(), Proposition::integers())
    ->call(function($a, $b) {
        if(equal_magnitude($a, $b) != (abs($a) == abs($b))) {
            echo "ERROR!! equal_magnitude is wrong when \$a is $a and \$b is $b!\n"; 
        }
    });

Oops! We're getting a lot of error messages. We will quickly discover that we used a = where we should have used a == in our function.

In practice, you will be using this to pass a huge, automatically generated range of values into your functions and check that some property always holds. You might for example want to check that the output of a function has a certain relationship to your input, that the function did or did not throw an exception, and so on.

Project goals

• Extremely lightweight and easy to use
  • You only need to use one class.
  • A simple trait for PHPUnit tests may be included in the future.
  • Dead simple API, which reads like English when you use good variable names.
  • Uses generators to produce randomized values which fulfill the given constraints.
  • Pragmatic: common use-cases already included like integers, integers within a range, strings, "garbage" data, etc.
  • But we do not need generators for every possible use-case. You are free to transform your values however you want in the callback to call, and you can use the Proposition::stream() method to generate values your own way.
  • Other than generators and callbacks, no use of "advanced" or "frameworky" features (there shall be no Proposition\Interfaces\PropositionableIterators\PropositionableIteratorInterface).
  • no packages in "require"
• Easy to integrate with PHPUnit but there should be NO functionality specific to that in the main Proposition class.
• Compatible with PHP v.7.0 and up but also v.5.6. Probably not below that.

Status

Most core functionality and documentation is complete. The plan is to fix issue #1 and issue #3, make some PHPUnit tests which test it with itself, then release it on packagist.

Contributors are welcome!