Technical Interview Part 2

Standard

What I do instead

Before technical interview session, a technical assignment given to the candidate on Friday, so that they can work on it over the weekend. The technical assignment typically takes few hours to complete. I have a range of questions from demonstrating a design pattern, build a simple application with database interaction, to SEO analysis algorithm.

The objectives of the technical assignment are:

  1. Ensure the candidate can codes.
  2. Evaluate how modern his development approach (for example, whether the candidate will use Elmah or Log4Net over writing a custom logger class)
  3. Evaluate how serious he treats his codes (if a candidate deliver a half-hearted solution, it indicates the same for his work codes)
  4. Evaluate whether he goes the extra miles (such as implementing unit tests and proper exception handling)

During the technical interview, I will do the following:

  1. Have the candidate to explain the core of the solution. I will then ask a few questions base on his implementation. For example if I want to implement certain change, where should I modify the code. This is to ensure I’m talking to the person who wrote the codes.
  2. Find a flaw in the system and press on it again and again – in a professional and respectful manner. This is to evaluate how well the candidate respond to criticism, whether the candidate get defensive and whether the candidate is open to feedback.
  3. Challenge the candidate on how he can upgrade his solution to be production ready on both code and infrastructure level. This is to evaluate how much thought he has given to his solution and how much of exposure the candidate has dealing with production system.

Next, I will move on to a list of generic topic on software development. Example of the topics I cover.

Source Control

Every developer uses source control to certain extend. I will normally ask what kind of source control has the candidate use. The top 3 answers are TFS, Git and SVN. I will ask the candidate to share with me, what are the differences between the top 2 source controls he is familiar with. The idea here is to discuss about what the candidate is familiar with so that he can show his best thoughts. Depending on what the candidate bring up to the table, I will get a sense of what kind of developer the candidate is.

For example, if a candidate tells me checking out a branch in TFS is downloading a whole new copy of the code; while Git is merely applying the delta difference on the same copy of the code, it indicates this candidate used to work with giant code base with some level of branching experience and he appreciates Git is much more efficient on client side storage.

Another example, if the candidate brought up terms such as Rebase, I will follow up by asking what is the difference between Rebase and Merge on theoretical level and when is a good scenario to use Rebase over Merge on practical level. Depending on the scenario given, I might (or might not) have further question to validate the usages. The idea here is I’m following up on the topics suggested by the candidate himself. If a candidate cannot provide solid evidence on how familiar is he with the topic suggested by himself, that indicates the candidate is throwing fancy terms around hoping to impress the interviewer.

Design Pattern

Despite the challenges I highlighted earlier on design pattern, I still think design pattern is a good topic to cover during technical interview because the right application of design pattern indicate the complexity of codes the candidates has dealt with, hence the need of design pattern.

Ever since I take the role of being an interviewer, I do make it a point to read up on additional design patterns that I have never used. The good news is, most candidates consistently brought up only a handful of design pattern. The top 3 are such as Singleton, Abstract Factory and Repository.

Although Dependency Injection is not strictly a design pattern, a lot of candidates did mention Dependency Injection as something they know under the design pattern topic. I do not dismiss this answer just because it did not fit into the definition. My objective here is to assess the candidate’s ability to design his code structure, not a competition of giving definition.

Singleton

What do I look out for during Design Pattern discussion? Take Singleton for example. After the candidate mentioned he knows Singleton, I will follow up with question “What is a good use case to use Singleton?”. The typical answer I got is something along the line “when you only need to have a single instance of the class”. Good. At this point, I know that the candidate is aware of the definition of Singleton although did not provide the use case I asked for. I will rephrase my question slightly differently to remind the candidate I’m looking for a use case.

One “interesting” answer always pop up is to apply Singleton in data layer (CRUD operation to database). I call this interesting because anyone who give a little more thoughts or have done some research in Singleton will realize it’s a bad idea to apply the pattern in data layer. However, this misconception comes up very frequently.

I will take this opportunity to explain to the candidate the kind of problem will surface for applying Singleton in data layer. Why do I do that? Having the right skill or information is important, but having the right attitude is equally (if not more) important. You can teach someone new skill but it is extremely challenging change someone’s attitude. At this point if the candidate appears to be enlighten with the new information, I know the candidate is coachable. In most situation, I would rather to have a coachable new hire (although not having the top notch skill set) over someone with superstar skill set but a poor attitude.

Database

Working with database will come across a developer’s path very frequently. It is an unspoken rule that a developer must be able to work with database. With the amount of storage options in the market, it is difficult to discuss all of them but we will stick with the most popular option for most .NET developer – SQL Server in this article.

When hiring a junior developer, the candidate will have to prove his ability in writing T-SQL. Insert, Update, Delete and different kind of joins. No big deal. For senior developer, I would normally ask the candidate what other exposure does he has apart from T-SQL. Asking the actual involvement in SQL Server gives me very good indicator what kind of system the candidate has dealt with.

For example, if the candidate claimed he takes care of database backup, I will follow up with what is the backup cycle and types of back up he was using. If all the candidate did was doing a full back up on daily basis, it indicates the database size he was dealing with was not very large and the data lost does not seem like a big deal which means the data is not extremely critical.

If the candidate mentioned he scales SQL Server, I will follow up with what type of replication he applied and what is the rational behind the decision. I will also ask what other strategies he has considered before using replication because replication is an expensive option. If the candidate brought up Redis cache and index provider such as Solr or Azure Search, it shows the candidate has looked beyond SQL Server context which indicates he is someone having very broad skill set across technologies.

Once a candidate told me he implemented table partitioning in his database. I asked what is the logical condition he applied his partition base on. He said primary key which is GUID data type. That was an interesting answer because the generally approach to create partition is to base on date or some other logical conditions. I explained to him how I would implement table partitioning instead and the reason behind it. His eyes were brighten up.

Notice that I did not say “This is wrong. The correct way is this”. Instead, I make it as a discussion on “This is what I will do instead”. The same information was delivered across, but the outcome will be very different.

The candidate impressed me because he knows about table partitioning that most developer don’t. It suggests that the candidate is someone who took the extra effort to learn new skills to solve problems. Most importantly, the way he responded to the information I shared with him suggests he is someone coachable. I took this candidate into my team and he has proven to be a star team member.

Few final thoughts…

There are a lot of other topics that I cover during the interview. Most of them are generic topics such as tweaking software performance and security. The purpose of having a standardized list of topic is to ensure I use the similar benchmark for candidates for the same position. The reason to start with generic topic and drill further down is to allow the candidate to talk about areas that they are familiar with so that they can showcase their sharpest thoughts.

When candidate brought up certain topic for discussion, I’m assuming he knows about the topic very well. I’m handing over the power to drive the discussion to the candidate to certain extend. I prefer to talk about what the candidate is familiar with (instead of mine) so that I can truly assess his level of technical competency. Frankly, there is very little value to talk about a topic the candidate has only read an articles on 6 months ago. However, whichever topics that the candidate brought up, I will drill really deep to ensure he indeed knows about them rather than just throwing some fancy words around. 

During technical interview, I’m looking at more than just technical skills. Technical skills is learnable. What really interest me are:

  • Whether the candidate is coachable?
  • How big of passion the candidate has over technology?
  • What is the candidate’s approach in solving problems?
  • What is the candidate’s attitude dealing with technology and PEOPLE?
  • How much of potential the candidate has so that the company can groom him to be a superstar developer and beyond?

The technical topics I have for the candidate were merely for me to expose those areas I’m interested to learn about the candidate. I’m never interested to know the difference between a clustered index vs non-clustered index or the difference between Azure Web Job vs Azure Worker Role vs Azure Function. Given a laptop with internet, anyone can Google them in 5 seconds. What I am interested to discover is whether this candidate is coachable, his passion, his approach, his attitude and his potential!

Ideally, we should hire the right person with the right skill. However such angels rarely come by. If I have to choose between the right person or the right skill, I will choose the right person any day. Of course, provided the candidate still has reasonable level of skill set on the role he is applying. New skills are learnable and very often it is very quick to learn a new skill. Coaching a person takes a much more time, energy and cha-ching – if you are lucky.

If you are not lucky, a bad apple not only bring down productivity but also break the current harmonious team. It is much more effective to filter the potential troublemaker than to “coach” or “develop” him later. There is no point hiring bad apples just to hit headcount. With people, slow is fast.

Some companies practice having a couple strong technical guys to interview candidates whom they might not eventually work with. The interviewers are hiring for the company wide. Some companies practice having the Team Lead / Architect within the team to interview the candidates whom they will eventually work with. They are hiring for the team. I have been in both the situations and personally I prefer to the latter.

Being able to work with the person whom I interviewed earlier will give me additional consideration and deeper thoughts into whether the candidate will be a good fit into my team. Another good reason is to allow me to validate and refine my interview techniques. Interview is all about perception and assumption made on the candidate. I have made good decisions and I have made bad decisions. However, in the situation where I made a wrong assumption base on a wrong perception, I can adjust my interview technique on a continuous basis if I have first hand experience working with the candidate I interviewed.

Finally, I don’t claim what I’m doing is the only way or the best way. We live and we learn 🙂 I found this approach to be working quite well hence I continue practicing. If you have any thought on this, please leave me a comment. Hope you have found something useful in this article. Until next time. Cheers!