The best replacement for testng is junit.

The best alternatives to testng are rated as following:
★★★★★  junit
★★★  junit selenium
★★  arquillian
★★  fitnesse
  jbehave

Your alternative for testng is not listed? Suggest!
Speaking about testng, one probably shouldn't forget about maven.

Other search terms related to testng and their ratings are:
★★★★★ maven
★★★★★ selenium
★★★★ ant
★★★ selenium webdriver
★★★ mockito
★★★ cucumber
★★★ jenkins
You have in mind a companion for testng and it is not yet here? Propose!



Google Trends

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testng
junit
junit selenium