Exterminators Week 5 - Pull Requests

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I have been running an experiment taking bigger changes and separating them into many MANY small pull requests. I am hoping to see the individual pull requests become easier and code to flow naturally. Larger changes should still be possible and be composed of several pull requests.

During the first few weeks with the Exterminators I noticed many of my pull requests becoming quite large and complicated. The code reviews I was doing for others were taking a long time. Many changes were included in each review and it was hard to evaluate the different parts affected. The reviews helped improve the code and lead to a better product, but felt like a bottleneck in the team’s process.

I am addicted to everything Continuous Delivery and have drunk the Kool-Aid. With my previous team we had been able to add new features and ship them into production later the same day. We kept all our changes small and in shippable sets which built upon each other. Code reviews were easier and could be done quickly by anyone on the team without compromising quality.

While the Exterminators cannot ship new features in a day, I thought I could use a similar approach to break down larger features into small changes which could be shipped independently or as a sequence. Individual changes could be broken down into small pull requests1.

For those following along, this fits in great with my focus and quality habits. I could focus intensely on one change at a time building toward larger larger improvements. As shown with my previous team, smaller reviews can be done more quickly. The individual changes could be tested and reviewed separately helping to reduce the risk of each change. Less risk leads to better outcomes and higher quality releases for our customers.

The Candidate

Ironically, when I started this new experiment I thought the defect I was working on would be incredibly easy! Initially it looked like a few line change at the most. I was fixing a defect similar to one we encountered in nearby code. I made the same change only to find it didn’t work!

After digging deeper into the problem I found even more issues and code duplication. I decided as I fixed the original issue I would also bite the bullet and refactor the code to remove the duplication. As an added bonus I could improve our test coverage to put a dent in our legacy code.

With fixing this defect, I had found a candidate for using small pull requests to solve a larger problem. Each pull request would bit by bit lead to the overall solution.

Finding A Starting Point

My first order of business was to decide where to start. I knew where the defect was caused, but wanted to plan my work so I could keep my changes safe. This was important because it would be hard to get enough tests in place to feel completely confident. Staying safe by isolating what was modified would also help me to focus on fixing the defect and only refactoring to eliminate the duplication without getting carried away.

In short I wanted to find a place in the code where I could come in, make my changes and get out without causing a mess.

I read thousands upon thousands of lines of code. Over time a picture emerged surrounding the code causing the defect. It was a gold mine and had everything I needed to get started. I could focus my testing above where the defect was caused and then surgically implement the fix. Everything I needed to do for the original fix could be done right at the place I found.

To make sure I was on the right path I quickly prototyped up a potential solution. The prototype worked and helped confirm my plan. Since I had taken many shortcuts for the prototype I then threw it out. I would then start again with small pull requests accompanied by automated tests.

Although my overall plan would address the defect and duplication, the starting point I chose would avoided areas not affected by the defect and most of the duplication. I wanted to focus on fixing the defect without distractions. This starting point would let me fix the defect directly. I could return to the other areas later and deal with the duplication.

Baby Steps

The first steps were slow, but were enough to start walking. I picked small adjustments at my starting point to help me better understand the code and make future updates safer. I added integration tests around the affected methods to make sure I did not break anything. I broke down a particularly confusing method into smaller pieces. I setup helper methods to access data I would need.

In order to minimize risk the changes were done with as much isolation from existing code as possible. Any unintended side effects could cause more defects and I thought the smaller the impact the better it would be. Even while breaking up the confusing method I tried to keep the majority of code intact, relying heavily on automated tools and small steps.

Things were going great, and then our release date happened. The actual fix was not ready. No problem. I wrapped up the changes I was making, tested them with the team and then shipped the first few pull requests. Rather than rushing out the fix we were able to slow down and make sure what we had already done was fully ready. I had planned for this eventuality and kept all the pull requests shippable.

Had I done the same changes all at once in one massive pull request this would have been a much riskier proposition. Naturally, more code would have been affected increasing the risk and what would need to be tested. Instead we tested the few updated components and surrounding areas. I felt great about my changes because they were low risk and surrounded by automated tests.

Into the Brink

With the release out of the way, I picked up the pace. By this point I had the complete plan for the change in my head and started to fill in the pieces. I implemented my new changes beside the old code using TDD. Instead of mixing my new updates with the existing classes I made new ones and tested them into submission.

After a few more pull requests I was able to fix the defect and integrate my changes with the rest of the system. Some of additions tried to isolate the new functionality, whereas others were created to highlight when new components were being integrated. Another pull request was used to rename a common component. Near the end I added a pull request to delete obsolete code.

Changes were cruising along and reviews were going well. The other developers were really getting into it. The collaboration was stellar. Then suddenly we hit a snag!


Unknown to us another team was working in the exact same area. It is an easy mistake to make and neither team considered the possibility of this happening. For several days before this happened, my small changes had been impeding their work and for the first time they merged before I did.

I was stunned. We had been going full speed only to be derailed at the last minute. It was disheartening to say the least. We were so close to finishing.

The more I looked at the other changes the better I felt. They had carefully and meticulously been doing many of the same things I had been trying to do, increase the test coverage and improve the code. In fact, the other developer also tried to tidy up the confusing method I broke down using a similar approach.

We regrouped and adjusted the remaining reviews based on the conflicting changes. Thanks to our small pull requests we were able to isolate what needed to be updated and then continue.

After we were done our final reviews and updates we took a breather. This gave time to full test the fixes. Overall the testing went fairly smoothly and soon we were ready to ship.


We didn’t stop there. We could have. It would have been easy. I wanted to finish the work we started and eliminate the duplication I had seen earlier. With the fix now complete we could switch back to work on the duplication we had found.

This time we tried to reduce how isolated the new changes were from the old code. Alternatively, we tried to break up the work along functional units to eliminate all duplication in one area at a time. Reviews would include more context and show new classes being used in the same pull request they were introduced. The earlier pull requests had a few occasions where it was hard to follow the changes flow across the many pull requests. The added context of these newer reviews would help this problem by clearly showing how new code was to be used.

Like before, we tried to keep some refactoring and deletions in their own pull request separate from cleaning up the duplication. These were some of the easiest reviews because they focused on a single change each and as a result were simpler than the others.

After these code reviews were complete, I did one last scan of everything merged together then did one final pull request to clean up some loose ends. Some classes could be moved around, renamed or have their visibility reduced. The many incremental steps made seeing the overall picture much harder. The final clean up let us tie everything together and review the finished product.

What Did I Learn?

I feel like I learnt a lot throughout the process and had fun doing it.

Over time I started to develop some general guidelines when creating each pull request. These came from going through the process and helped provide direction for the individual changes.

  • Balance impact to existing code and establishing a context.
  • Reduce the risk and make safe changes.
  • Don’t do very much at a time.
  • Solve one part of the problem. Repeat.

Using small pull requests and many code reviews helped focus our development. We gained momentum as we kept going and were able to streamline the changes. Despite working in small increments, we managed to perform a moderate refactoring and fix defects safely. The code is better off thanks to the work we did and has better test coverage.

Each step of the way I would have felt comfortable shipping what we had merged. Even when we were reset in the middle of our work we were able to adjust our changes and continue. In fact having our pull requests interrupted by another merge has made me believe doing small frequent pull requests makes dealing with merge conflicts easier.

Even now, weeks after the changes were wrapped up we are still learning from the experiment and ensuing discussions. I would definitely do it all over again and have several times in the subsequent weeks. Others on the team have tried variations on the same idea. Our reviews have been a very vibrant retrospective topic and I am sure we will continue to explore the ideas we first tried here.

Would you try the same approach for your work? Would using small pull requests help you ship better? Give it a shot! I hope you like it.


1. I use the term pull request quite a bit throughout this post interchangeably with code review. Pull requests are a common process that looks a little like this:

  1. Have an idea
  2. Branch the code
  3. Do your work on the Branch
  4. Get the branch code reviewed (and address any issues/recommendations)
  5. Merge the Branch
  6. Repeat

For nice simple tutorial show the entire pull request process using plain git see Effective pull requests. The article shows all the major mechanics for doing pull requests using branches and even a few advanced techniques and tools.

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