Refactor like a PRO

The art of continuous, safe and aggressive refactoring

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Motivation

The best developers I work with share this same habit:

They refactor code as they touch it

But what is refactoring? Refactoring isn't something you do at the end of every sprint. It’s also not something that you need to ask permission for. It also doesn't mean rewriting your entire application.

Refactoring is an act of improving the structure of a code without modifying its behaviors. It’s a stream of small changes. It’s a continuous practice you do whenever you touch the code. Always.

When we do refactoring, our goal is to:

• simplify design

• improve namings

• identify and remove code smells

• use design patterns for common problems

• improve testability and maintainability

Writing clean code and keeping it clean is only possible by practicing continuous refactoring. Here are my top 7 tips to become a PRO in refactoring:

1. Do aggressive refactoring at small scales

When I work with developers, I notice two common mistakes related to refactoring:

• They refactor at a large scale all at once

• They don’t run their tests continuously

To practice aggressive refactoring at small scales, do the following:

1. Refactor a little piece of code

2. Run all your tests

3. Repeat 1-2. until your code is in a good shape

By refactoring a little piece of code you can make only small mistakes that are easy to correct. By running all your tests, you can ensure you didn’t change any behavior.

If you can’t run all your tests frequently because they are slow, fix that first. Your unit test suite should run within a few seconds, at max. To run your tests continuously, use continuous test runners like:

• NCrunch for C#

• Wallaby.js for JavaScript

• PyCrunch for Python

• Custom file watcher to trigger test execution

Nothing will give you more confidence during refactoring than running your tests all the time.

2. Master the refactoring hotkeys of your IDE

The best developers I work with know the refactoring hotkeys by heart. Next to increasing productivity, it makes coding fun. There is no better feeling than refactoring code with hotkeys than seeing your tests passing in the end. Passing tests are dopamine ✅✅✅

Built-in refactoring tools also make refactoring safer. Here are the most common hotkeys I use daily:

• Rename

• Move line

• Inline variable

• Extract to method

• Introduce variable

• Introduce parameter

• Change function signature

Know these hotkeys by heart!

3. Use mutation testing before refactoring code

The biggest risk of refactoring is that we can break existing functionality. But it can only happen if you have low-quality tests. To improve tests, many people use code coverage tools, mistakenly. Code coverage is not a quality metric. It can help detect untested areas of the code, but it doesn't tell anything about the tested areas.

How can we improve the quality of our tests then? The answer is: Mutation Testing.

Before you refactor poorly tested code, you should run Mutation Testing to verify that your tests are reliable. Learn more about Mutation Testing in my previous post.

4. Turn comments into well-named components

Code comments are code smells:

• ❌ They are never compiled or executed

• ❌ They become easily outdated and rotten

• ❌ If used extensively, nobody reads them

But there are a few exceptions when they make sense:

• ✅ Explaining the why

• ✅ API doc generation

• ✅ Revealing implicit behaviors

Apart from these, don't write comments. Use intention-revealing names instead. Turning comments into well-named functions and classes is a cheap and easy win while refactoring code.

5. Follow the Rule of Three

It’s completely fine to have duplicated code. Duplication is far cheaper than wrong abstractions. But one can still improve code by removing duplication with the Rule of Three. This rule suggests that a piece of code should be extracted into a separate component only if it’s repeated three times. It strikes a balance between premature optimization and excessive duplication.

Note that you should only remove duplication if the identical pieces of code represent the same business knowledge. Otherwise you introduce risk. Here is why:

6. Don't mix refactoring with changing behavior

The are many problems with changing behavior while refactoring code such as:

• Adding risk

• Increasing mental load

• Making code review harder

• Making bug-finding difficult

• Making our actions error prone

Focus on one thing at a time. Either refactoring or changing behavior. Never both. Take baby steps. To keep refactoring separate from changing behavior, use Test-Driven Development (TDD).

7. Use TDD to make refactoring a core part of development

After all, we all tend to forget to do refactoring. There is time pressure or we are just too lost in writing code. But TDD fixes this. It has a dedicated phase for refactoring. It reminds you to refactor your code in every cycle. It encourages baby steps which keeps your refactorings small and safe. Learn the other benefits of TDD from my previous post.

Conclusion

Most software engineering problems don’t come from not using the latest frameworks or not utilizing the best algorithms. Most engineering problems come from the mess we have in the code.

Refactoring is not a separate activity. It’s a fundamental part of software development. Refactor code early and often. Refactor it aggressively. Refactor it continuously. Run your tests all the time. And refactor safely with the help of TDD and mutation testing.

Never forget: the cost of refactoring a bad design is cheaper than the cost of living with it.

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