Testers have always faced a typical challenge. They work in silos. Hence came the concept of Pair Testing. It is a software testing technique that promotes two or more testers to test one feature of the software, at the same place and same time. It is believed to encourage ideas when both the testers interact and make suggestions to each other for a better outcome.

One of the key reasons that more organizations are adopting this unique testing technique is that it enhances productivity of new testers eventually as an experienced tester works closely with the newbies. It serves as an excellent way to mentor and train new testing personnel in the team while working on the project. Pair Testing also helps to better gauge the performance of the testers when they are working in groups. It is an open-ended defect detection method and proves to be highly cost-effective. There is better collaboration and coordination between team members and teams can collectively enhance domain knowledge.

Source: http://qatestlab.com/knowledge-center/software-testing-glossary/Pair-Testing/

Also known as session-based training, it is not important to have complete test cases to start testing in pairs. You can start even if you have ready checklists or even test ideas.

However, some of the drawbacks of this form of testing are that a tester cannot write the bug report till the entire session is over. Writing a report afterwards can become cumbersome and take more time than usual. Also, it might be difficult to show the productivity from the combined efforts to the management. Clearly, the best takeaway of the Pair Testing technique is that training can be completely skipped.