TestNG Reports are the default HTML reports which are generated once the test cases are executed using TestNG. These reports help you to identify the information about test cases and the status of a project. TestNG reports in Selenium have three methods passTest, failTest, and skipTest to check the data about test cases.
Extent Reports is an open-source reporting library useful for test automation. It can be easily integrated with major testing frameworks like JUnit, NUnit, TestNG, etc. These reports are HTML documents that depict results as pie charts. They also allow the generation of custom logs, snapshots, and other customized details.
Emailable Reports is the summarize report of the current test execution which contains Test Case message in green (for pass test cases) and red(for failed test cases) highlight.