There are several different types of testing tools (or frameworks) available for PHP, which use different approaches – all of which are trying to avoid manual testing and the need for large Quality Assurance teams, just to make sure recent changes didn’t break existing functionality.
Test Driven Development
Unit Testing is a programming approach to ensure functions, classes and methods are working as expected, from the point you build them all the way through the development cycle. By checking values going in and out of various functions and methods, you can make sure the internal logic is working correctly. By using Dependency Injection and building “mock” classes and stubs you can verify that dependencies are correctly used for even better test coverage.
When you create a class or function you should create a unit test for each behavior it must have. At a very basic level you should make sure it errors if you send it bad arguments and make sure it works if you send it valid arguments. This will help ensure that when you make changes to this class or function later on in the development cycle that the old functionality continues to work as expected. The only alternative to this would be
var_dump() in a test.php, which is no way to build an application – large or small.
The other use for unit tests is contributing to open source. If you can write a test that shows broken functionality (i.e. fails), then fix it, and show the test passing, patches are much more likely to be accepted. If you run a project which accepts pull requests then you should suggest this as a requirement.
PHPUnit is the de-facto testing framework for writing unit tests for PHP applications, but there are several alternatives
Integration testing (sometimes called Integration and Testing, abbreviated “I&T”) is the phase in software testing in which individual software modules are combined and tested as a group. It occurs after unit testing and before validation testing. Integration testing takes as its input modules that have been unit tested, groups them in larger aggregates, applies tests defined in an integration test plan to those aggregates, and delivers as its output the integrated system ready for system testing.
Many of the same tools that can be used for unit testing can be used for integration testing as many of the same principles are used.
Sometimes also known as acceptance testing, functional testing consists of using tools to create automated tests that actually use your application instead of just verifying that individual units of code are behaving correctly and that individual units can speak to each other correctly. These tools typically work using real data and simulating actual users of the application.
Functional Testing Tools
Behavior Driven Development
There are two different types of Behavior-Driven Development (BDD): SpecBDD and StoryBDD. SpecBDD focuses on technical behavior of code, while StoryBDD focuses on business or feature behaviors or interactions. PHP has frameworks for both types of BDD.
With StoryBDD, you write human-readable stories that describe the behavior of your application. These stories can then be run as actual tests against your application. The framework used in PHP applications for StoryBDD is Behat, which is inspired by Ruby’s Cucumber project and implements the Gherkin DSL for describing feature behavior.
With SpecBDD, you write specifications that describe how your actual code should behave. Instead of testing a function or method, you are describing how that function or method should behave. PHP offers the PHPSpec framework for this purpose. This framework is inspired by the RSpec project for Ruby.
Complementary Testing Tools
Besides individual testing and behavior driven frameworks, there are also a number of generic frameworks and helper libraries useful for any preferred approach taken.