Spock vs TestNG comparison of testing frameworks
What are the differences between Spock and TestNG?

	Spock http://spockframework.org/	TestNG https://testng.org/doc/documentation-main.html
Programming language	Java	Java
Category	Unit Testing	Unit Testing, Intergration Testing, End-to-End Testing
General info	Spock is a testing and specification framework for Java and Groovy applications Spock has a highly expressive specification language, and due to its JUnit runner, Spock is compatible with most IDEs, build tools, and continuous integration servers.Spock is inspired from JUnit, RSpec, jMock, Mockito, Groovy, Scala, Vulcans among others	TestNG is a testing framework for the Java programming language inspired by JUnit and NUnit TestNG is similar to JUnit and NUnit but with newer functionalities such as: annotations, test that your code is multithread safe, flexible test configuration, support for data-driven testing (with @DataProvider), support for parameters, powerful execution model (no more TestSuite) and more... It's also designed to cover all categories of tests unit, functional, end-to-end, intergration... etc
xUnit Set of frameworks originating from SUnit (Smalltalk's testing framework). They share similar structure and functionality.	No	No
Client-side Allows testing code execution on the client, such as a web browser	Yes Spock tests front-end components and functionality by unit testing individual classes and functions	Yes The scope of testing with testNg is wide and you can test various front-end functionalities and behaviours with it
Server-side Allows testing the bahovior of a server-side code	Yes Spock tests back-end components and functionality by unit testing individual classes and functions	Yes You can test server-side functionalities and behaviours with TestNg
Fixtures Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test	Yes Spock contains four methods for setting up environments :setup() (run before every feature method), cleanup() (run after every feature method), setupSpec() (run before the first feature method), cleanupSpec() (run after the last feature method)	Yes Fixtures are inbuilt into testNG, these are the annotations which are: @BeforeSuite, @AfterSuite, @BeforeTest, @AfterTest, @BeforeGroups, @AfterGroups, @BeforeClass, @AfterClass, @BeforeMethod, @AfterMethod
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 You can use the fixture methods to setup environments for groups of tests.	Yes You can use various fixtures to setup environments for group tests
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	N/A
Licence Licence type governing the use and redistribution of the software	Apache License 2.0	Apache License 2.0
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 Spock has inbuilt mocking capabilities and has no need for external libraries	Yes By Use of an external library like mockit which intergrates well with testNG
Grouping Allows organizing tests in groups	Yes You can create suites manually in spock	Yes Multiple test cases can be grouped more easily by converting them into testng.xml file, in which you can make priorities which test case should be executed first
Other Other useful information about the testing framework