Braintree interview questions

Phone Screen interview with Recruiter, and reviewed code challenge submitted remotely. The Recruiter asked about background and gave some insight into the company, their benefits and where they are going over the next year.

They've sent me the interview request on Hired.com. After the initial phone conversation with their recruiter he sent me the test assignment to be completed within 5 days. The tests and README are required besides just the implementation, note that later on during an on-site pairing session you'll continue working on this same program and you'll have to explain your solution to their developers. Looking back I must say not being able to TDD it while extending the functionality on-site would probably be a "no". I've TDDed every line of the code in Ruby from start to finish and it was a pleasure since the task is simple enough to work with value objects which can be easily unit tested. Also it's possible to write an acceptance test for the program with the help of a gem that provides some particularly helpful Cucumber steps. I've sent the solution and in three days their feedback was that they liked it and we scheduled a phone interview with their developers. The questions during a technical phone interview were all standard. I've passed it and they've invited me to San Francisco for a full-day 4-session on-site interview. Those are 1. Another tech interview. 2. Lunch. 3. Pairing session to explain the solution to the coding assignment, extend it with new functionality and showcase your Unix skills on a live box. 4. Product session where you'll have to go through building a sample web app (e.g. Amazon, Tinyurl, Ticketmaster, Eventbrite and so on). Keep in mind that this is purely technical session and they'll try to see the depth in all aspects of the construction of an app and how would you resolve some edge cases like when two people are booking the same seat at the same time. At the end they asked how would you scale the app. I've successfully passed the lunch and a pairing session, but failed at a tech and product sessions by not answering some naive questions like what's the difference between the optimistic and pessimistic locking, what's the difference between "includes" and "joins", how passwords are hashed/salted during an authentication, some Ruby object model questions and a couple of others. So if you're confident in Ruby, Rails, database layer (including key/value stores) and TDD, you should be fine.