If you can download the testng plugins, create in your dropins directory a structure similar to this one

/path/to/mydropins
      testng-eclipse-x.y/
         eclipse/
            features
               org.testng.eclipse_x.y.z.jar
            plugins/
               org.testng.eclipse_x.y.z.jar

With 'path/to/mydropins' a shared dropins repository referenced in your eclipse.ini with a:

-Dorg.eclipse.equinox.p2.reconciler.dropins.directory=/<myPath>/mySharedDropins

You need to copy both:

• http://beust.com/eclipse/features/org.testng.eclipse_5.14.10.20110228_1533.jar
• http://beust.com/eclipse/plugins/org.testng.eclipse_5.14.10.20110228_1533.jar

was facing same issue as i was unable to install same from market and install option. Finally it helped me to sole the issue by following 3rd method listed in below link.

https://www.techbeamers.com/install-testng-in-eclipse-ide/#method3

Install TestNG In Eclipse IDE Via Offline Jar Files.

First step:

Firstly download the latest TestNG Jar files from the link given below. We’ve provided the direct URL to download the TestNG version 6.11.

Clicking on the link will download the “site_assembly.zip” file for the TestNG version 6.11. This file contains two folders named as “features” and “plugins“.

The features folder contains the following two files.

org.testng.eclipse.maven.feature_6.11.0.201703011520.jar org.testng.eclipse_6.11.0.201703011520.jar The plugins folder contains these two files.

org.testng.eclipse.maven_6.11.0.201703011520.jar org.testng.eclipse_6.11.0.201703011520.jar Note – You can check for more recent releases of TestNG

Second step:

Go to the eclipse installation directory and look for the “dropins” folder there. Create a folder inside the dropins folder and name it as “testng-eclipse-6.11“. 6->Major version & 11->Minor version of the TestNG plugin.

Extract the “site_assembly.zip” file and copy its content i.e. the “features” and “plugins” folders to the newly created “testng-eclipse-6.11” directory. The eclipse install directory would now look like this or similar to this.

C:\Users\techbeamers\eclipse jee-neon\ dropins\ testng-eclipse-6.11\ features\ org.testng.eclipse.maven.feature_6.11.0.201703011520.jar org.testng.eclipse_6.11.0.201703011520.jar plugins\ org.testng.eclipse.maven_6.11.0.201703011520.jar org.testng.eclipse_6.11.0.201703011520.jar

Note – We’ve tested this option with the Eclipse Neon/juno version.

Third step:

Last but not the least, you will need to restart or start the Eclipse to see the TestNG plugin getting loaded into the IDE. However, the process would be slightly slow as the Eclipse will first time load the new plugin.

From Eclipse, by pressing CTRL+N, you can open the “New” wizard. It will load the list of all available module/project templates. By scrolling down in the list, you can make sure that it has the “TestNG” option.