7 best PHP Assertion libraries in 2025

PHP asserts are used to make sure the code is working as expected. They are used to ensure that certain conditions are met and that the code is doing what it's supposed to be doing. An assertion is a statement in code that evaluates whether its condition is true or false. If it returns true, the program continues its execution, or else it throws an error. PHP Unit Testing consists of Assertions and the first step to doing unit testing is to write assertions for your code. Assertions are used for Test-Driven Development (TDD) and Behavior Driven Development (BDD). In this kit, we will go through the top 7 best PHP assertion libraries that you can use to write assertions for your code assert - validate method input/output with nice error messages; phpunit-snapshot-assertions - A way to test without writing actual test cases; SwaggerAssertions - API requests and responses match with your swagger definition.