PHPUnit vs RSpec comparison of testing frameworks
What are the differences between PHPUnit and RSpec?

PHPUnit

https://phpunit.de/

RSpec

https://rspec.info
Programming language

PHP

Ruby

Category

Unit Testing

Unit Testing, Intergration Testing

General info

PHPUnit is a unit testing framework for the PHP programming language

PHPUnit is a programmer-oriented testing framework and is an instance of the xUnit architecture for unit testing frameworks.

Domain Specific Language (DSL) testing solution for Ruby code

It focuses on empowering Test Driven Development (TDD). RSpec contains multiple smaller libraries, which may be independently used with other testing frameworks.
xUnit
Set of frameworks originating from SUnit (Smalltalk's testing framework). They share similar structure and functionality.

Yes

It's an instance of the xUnit architecture for unit testing frameworks

Yes

Yes, but it differs from more traiditional xUnit solutions. Its tests are written in a "Tests as Specification" manner. This means that the terminology used in RSpec is adjusted to a language more fitting for specification.
Client-side
Allows testing code execution on the client, such as a web browser

Yes

It can perform Unit tests and can test various front-end components and behaviours

Yes

RSpec is used to primarily test the behaviour of applications or individual components so it can test front-end behaviour as well - you can use capybara gem with RSpec for that.
Server-side
Allows testing the bahovior of a server-side code

Yes

By performing unit tests on singular back-end components

Yes

You can test server-side behaviour with Rspec
Fixtures
Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test

Yes

By use of a setup code. The setup code consists of two Important template functions, the 'setUp()' function (called to create the objects to be tested) and 'tearDown()' function (called to cleanup the objects which you tested)

Yes

RSpec does contain fixture methods
Group fixtures
Allows defining a fixed, specific states of data for a group of tests (group-fixtures). This ensures specific environment for a given group of tests.

Yes

It does support group fixtures

Yes

Group fixture methods are supported
Generators
Supports data generators for tests. Data generators generate input data for test. The test is then run for each input data produced in this way.

N/A

Yes

RSpec contains generators for example intergration_'test_name' which will save a spec inside the spec/requests folder
Licence
Licence type governing the use and redistribution of the software

Creative Commons Attribution 3.0 Unported License

MIT License

Mocks
Mocks are objects that simulate the behavior of real objects. Using mocks allows testing some part of the code in isolation (with other parts mocked when needed)

Yes

One of its main features is that PHPUnit comes with out of the box support for Mock objects

Yes

Available through rspec-mocks gem.
Grouping
Allows organizing tests in groups

Yes

It allows grouping of tests and by using the @group annotation one can tag a test to belong to one or more groups

Yes

Allows declaring example groups and contexts.
Other
Other useful information about the testing framework