Code Review Essentials

Friday, June 3rd, 2022

Code Reviews are an essential part of Software Engineering, providing numerous benefits for teams and the products they deliver. Having spent a significant amount of time conducting them for many years now, in this article, we will touch upon some key aspects to consider which, generally speaking, are of particular importance.

Similar to functional testing, Code Reviews provide a unique set of quality controls which help ensure standards are upheld; affording teams the ability to verify a number of critical concerns early on and within the confines of engineering specific constructs. This almost certainly yields a higher return as the time investment required to address issues at this stage requires minimal involvement across teams and functions.

Code Reviews also serve to aid in the verification and upholding of best practices, standards, and conventions across teams and within organizations. These standards can cover a broad range of concerns such as consistency, facilitation of reuse, scalability, security, optimization, readability, simplification, and any other auxiliary criteria specific to a given organization.

Additionally, the Code Review helps to confirm that requirements have been fulfilled in the context of the underlying feature being reviewed as, it is not uncommon for developers to misinterpret requirements.

Likewise, developers are generally focused on solving various small problems in a very particular and limited scope. Because of this, it is inevitable that opportunities will be missed, and oversights will be made. One of the primary responsibility of the Reviewer is to provide a holistic and broad perspective which takes into account not only the soundness of the code being reviewed, but also how it measures, complies, and integrates in the context of the larger system as a whole.

By having another set of eyes, so to speak, we arm ourselves with a very important second line of defense, as well as an agent for opportunity.

One of the most beneficial aspects of Code Reviews is the investment in overall knowledge throughout the team; and ultimately, the ROI it provides. As such, core to the Code Review is the proliferation of knowledge. This applies to both the Reviewee, and the Reviewer alike.

For the Reviewee, when areas of improvement, best practices, optimizations, abstractions and the like are outlined, an opportunity is presented for one to learn new (often improved) techniques which they may not have been aware of otherwise. This holds particularly true for more junior developers who simply have yet to acquire the experiential knowledge obtained by their more senior counterparts. By learning from the experiences of others, the Reviewee can expedite their own growth as a Developer. Here, the expectation is that, overtime, each Reviewee will have fewer and fewer of the same review comments to address as they now have a dedicated platform (even if unofficially so) from which to continually learn.

For the Reviewer, Code Reviews provide an opportunity to share knowledge and insight, while affording one the ability to obtain a broader understanding of the system in its entirety, as this knowledge is vital to providing a successful review.

Additionally, it may be necessary for a Reviewer to devise and provide solutions to problems which the may not have encountered previously and, in order to be effective, a Reviewer must be confident in the feedback and solutions they are providing. This alone affords the Reviewer themselves the ability to gain a deeper understanding of their own knowledge, while also challenging themselves in order to obtain the information necessary to do so. Thus, for the Reviewer, Code Reviews present a tremendous opportunity to not only provide value to others, but also to obtain and enhance their own value as well.

In general, developers more or less tend to work in a rather silo’d manner, primarily focusing on one particular problem space (particularly in the scope of a given feature), and only collaborating when necessitated by DSMs, meetings, or when they or another team member runs into a problem and needs assistance. While much of this is a rather natural by-product of feature development, so to, can it be said that Code Reviews naturally cultivate collaboration; thus, collaboration can be built into our processes by default.

With Code Reviews, no one Developer is ever working completely on their own. This has numerous benefits, many of which have already been outlined above, yet perhaps one of the most significant benefits is that developers are much more likely to double check their work and submit something that they can be proud of when they know someone else on their team will be reviewing their work. Likewise, Reviewers, no matter how experienced, are much more likely to validate and double check their feedback for the exact same reasons. This alone lends itself to higher quality output across the board.

Key Aspects to Consider

While numerous aspects must be considered with respect to conducting Code Reviews, generally speaking, there are common considerations which by and large tend to hold true. While certainly not an exhaustive treatise, what follows is a brief outline of those I have found to provide particular value.

Atomicity: PRs should be atomic (relatively small in nature). If PR is excessively large, it should be rejected and the engineer should be informed to break out the PR into smaller submissions (generally these smaller submissions can be merged to an intermediary branch before being merged to the intended target branch). This is crucial as the surface area for mistakes and missed opportunities is proportional to the amount of code being reviewed. In addition, requiring PRs which are smaller in scope encourages developers to think in terms of smaller units of function and subsystems, which in turn leads to clearer separation of concerns, and encapsulation. As such, it is often helpful to impose a change threshold for submitted PRs.

Compatibility: Changes should remain backwards compatible and not introduce breaking changes (unless expressly coordinated across teams). Reviewers need not checkout each PR and explicitly test each feature being submitted, rather, they should always be cautious of breaking changes, particularly in terms of APIs (e.g. argument positions changing, etc.).

Consistency: PRs must fully adhere to well documented and established standards and conventions; typically supported via commit convention tooling. This is crucial as, consistency and conformity of standards leads to a unified codebase where developers can easily work across packages and features with very limited effort as, the overall structure and coding style is consistent; making it much easier to know where everything should, and is, defined, how modules are organized, and readability is immediate as formatting and structure remains the same across packages and modules.

Clarity: All modules, functions, classes, types, etc. are always be clearly named, defined, remain properly encapsulated, and reside within a logical and appropriate location.

Readability: Readability should be favored over excessive succinctness or overly “clever” implementations which do not read well. Conversely, overly verbose implementations are to be avoided as well. It is important to remain cognizant of the fact that code is read many, many more times than it is written. Moreover, when implementations become hard to reason about, that is often a sign of a poor implementation (usually the result of a specific unit doing too far much). Succinct, yet meaningful names must always be used. Strive to ensure code is self documenting in terms of its intention.

Reusability: Implementations must take reuse into account at all times; be it abstractions to common packages, abstractions within a particular project, or abstractions within a particular scope of a project. In addition, Reviewers should always be on the look out for additions which are redundant and should be removed and replaced with existing APIs available. This includes both internal APIs, as well as third-party libraries. Always ensure native APIs are being leveraged (Array.forEach, etc. rather than explicit for loops) as well as standard third party libraries (lodash.debounce, etc. rather than custom implementations). No redundancies should be introduced, and implementations should fully utilize existing APIs, Modules, Components, etc. throughout the available packages.

Simplicity: Solutions should always be implemented in the simplest way possible. Less is more, this extends down to each line of code. Keep things as simple as possible, but no simpler.

Scalability: Implementations must be performant and optimized to an acceptable and expected level – generalized optimizations must be made, and premature optimizations should only be suggested when necessary.

Securability: Implementations must be secure, keeping standardized security measures in place and ensuring attack vectors and cumulative surfaces are fully understood, accounted for, and securely addressed.

Discoverability: Documentation and / or related tools should follow specific conventions and remain succinct and to the point. Ideal documentation should provide a meaningful, yet brief description, followed by a useful example which speaks for itself (often, unit test expectations can be used verbatim here). On a related note, sources should not contain overly verbose inline comments as well. When, for example, a function has more lines of inline comments than actual implementation code, that’s usually a sign that the code does not read well, or the developer has merely been leaving “note to self” comments. In such cases, strive to provide ways to simplify the implementation such that it achieves better readability by being self documenting.

Accountability: It is crucial that all Team members are aware of the criteria against which their code will be reviewed as, doing so essentially holds developers accountable for ensuring they not only understand what is expected, but are diligent in reviewing their own work prior to submission. Developers should be encouraged to pre-submit PRs for performing a “self review” prior to officially submitting and / or assigning a reviewer. This approach is quite valuable as it provides the developer with a high-level overview of their changes outside of the environment they have been working in, and within the context of the branch to which their changes will be integrated.

While there are certainly other factors to consider when conducting Code Reviews, the above considerations touch upon some of the more fundamental aspects, with the key points hopefully being apparent as, perhaps the most important trait of a successful reviewer is in one’s ability to clearly express intent while also passing this knowledge on to others.

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