My current project has undergone an highly protracted round of interviews due in part to the hiring freeze that for some strange reason started in September.
This was my first set of interviews where I used pair programming as part of the interview process.
It was extremely effective. We used a highly simplified 'story' to test the candidate's design and coding skills. The story defined an UserManager middleware component that was used to register new users given a login and an e-mail address. The inputs were to be validated and an e-mail sent to the e-mail address containing an auto-generated password.
An empty Eclipse or IntelliJ project was provided with Spring, JUnit and all the mocking frameworks available as dependencies. A working Maven 2 build was implemented on the command line. The candidate was asked to provide an implementation of the middleware component and provide interfaces for all the dependencies that this component required.
There were two interviewers with the candidate, one acting as pair and the other as the product owner.
We were looking for a clear understanding of interface-implementation separation, understanding of how unit testing and dependency injection fitted together and a clear understanding of the IDE tooling and the various refactorings.
It was certainly effective. It was surprising how many candidates that seemed technically competent verbally were unable to make any headway with this exercise. A lot of candidates just couldn't handle the unfamiliar interview situation; others really had not learnt the tools of their trade and were unable to use the IDE to speed up their coding; other candidates had claimed TDD experience and were unable to write a decent unit test or use mocks; many candidates were unable to handle the design element, defining interfaces and making clear, logical decisions about contracts and responsibilities.
The successful candidates usually sketched out the domain either as interfaces in code or on paper, they asked good questions of their pair and the product owner and they always were very clear about what testing was needed. They also picked up the fact that the story was incomplete and asked about details of the validation.
A pair programming interview highlights the candidates technical skills but provides great insight into their characters and how they will fit into a team.
