Hamcrest is a set of matchers for writing more expressive code. It just so happens that these matchers are especially useful when writing tests. In this article, we'll look at Hamcrest for PHP. [...] Hamcret's expressiveness originated with JMock, but it wasn't until the addition of the unique assertThat() method that it was refactored into a self-contained library and independently usable in testing frameworks.

He talks about the "generations" of unit testing tools, a division based on their assertion functionality - simple, exact or using matchers. Installation instructions via PEAR are included (though there's also a composer package for it too) as well as code for an example test. More samples are given for comparing things like numeric values, strings and setting up inclusions and exclusions with the anyOf/noneOf matchers.

There are a number of situations where matchers are invaluble, such as UI validation, or data filtering, but it is in the area of writing flexible tests that matchers are most commonly used.

His example that checks to see if one object is equal to another object. The Hamcrest matcher allows for a "assertThat" method making it easier to create and use pre-existing unit testing assertions.

He also includes a list of some of the most common matchers broken up into groups of core, logical, object, number and text.

I have begun to port Hamcrest, which provides a library of matcher objects (also known as constraints or predicates) allowing "match" rules to be defined declaratively, to be used in other frameworks. Typical scenarios include testing frameworks, mocking libraries and UI validation rules, to PHP.

The hamcrest-php project compliments other current hamcrest-related projects and his ultimate goal is to make it available to the PHPUnit testing community (as well as with the PHPMock effort).