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

Robot Framework

https://robotframework.org/

TestNG

https://testng.org/doc/documentation-main.html
Programming language

Python

Java

Category

Acceptance Testing

Unit Testing, Intergration Testing, End-to-End Testing

General info

Robot is a Python framework used for acceptance/functional testing

Robot is an automated test framework which has a simple plain text syntax and can be extended easily with Python or Java libraries. It can run on the .net-based IronPython and on Jython which is Java based.

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

Robot has a rich library and can also be easily integrated with Selenium for browser automation to test front-end components

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

Robot can be used for back-end tests as well

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

There is no inbuilt way to work with fixtures in Robot however it can integrate with unittest and use fixtures that way

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.

By integrating with unittest

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.

Yes

Robot has a library called the Robot Framework Faker library. It contains 147 keywords used for generating random test data

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

Robot can access Python's mock library for mocking

Yes

By Use of an external library like mockit which intergrates well with testNG
Grouping
Allows organizing tests in groups

Yes

One can create a test suite with Robot

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