Shift Left Testing: A Complete Guide 

Despite a constant influx of new tools aimed at helping software development teams become more productive, companies continue to struggle to optimize the speed and efficiency of their development processes.  

A 2022 Infragistic survey shows that 31% of developers believe that they don’t have enough time to get their work done. About 40% say that high customer expectations and increased customer demands are the two most significant challenges they face.  

One reason developers have difficulty delivering projects on time is that they are spending too many working hours fixing bugs instead of creating new code. 

A recent Rollbear survey found that 32% of developers claim to spend up to 10 hours a week focusing on bug fixes, and 55% say that if they didn’t have to fix bugs, they would have more time to build new features and functionalities. 

What can developers do to decrease the number of bugs that appear after deployment? Proponents of shift left testing argue that the solution lies in altering how and when you perform code reviews and testing. 

Let’s take a deep dive into the concept of shift left testing to understand how it works, its benefits, and how your team can implement these ideas to improve software quality.

What Is Shifting Left Testing?

Instead of waiting for your code to be ready for deployment before testing it, shift left testing encourages reviewing and testing your code early and often in the development process. 

The etymology is this: Since most Western languages read from left to right, the earliest phase of a sequence is represented on the far left of the spectrum. However, shift left testing doesn’t just mean that code should be tested in the earliest phases of development. Instead, testing should be continuous and iterative throughout the entire software development lifecycle (SDLC).  

To understand how and why this movement began, we must first understand the history of the SDLC. The term “shift left testing” is relatively new, coined by Larry Smith in his 2001 paper of the same name.  

Before shift left testing originated, software development was generally a sequential and linear process in which testing was performed in the later stages of the SDLC, typically right before deployment. This is often referred to as the “waterfall method.” One of the most cited examples of this methodology is Winston Royce's 1976 paper, "Managing The Development of Large Software Systems.”

A typical software development process following the waterfall method of development might include the following steps: 

1. 1. Your product team performs market research and customer surveys to gain a better understanding of what needs to be created. 
      
      
   2. User stories and product specifications and requirements are created. 
      
      
   3. A development roadmap is created. 
      
      
   4. Development teams assess the roadmap and requirements. 
      
      
   5. Tasks are assigned, and developers begin coding.
      
      
   6. The code is tested once the features have been built.
      
      
   7. Found issues and bugs are fixed. 
      
      
   8. The code is deployed. 

But what happens if a large number and variety of complex problems are identified during testing? Now, you’re no longer testing for a few days and deploying. You could spend a week or more testing, identifying problems, reporting them, researching them, fixing them, and retesting your code.  

Shift left testing argues that if you test early and often in the software development process, you’ll have fewer bugs to fix later, saving your team time and decreasing the chances of deploying buggy code. 

In shift left testing, testers are encouraged to be present in planning sessions and to understand feature requirements and timelines as much as developers. Developers are encouraged to perform their own unit tests and code reviews as they code, catching and fixing minor errors as they test earlier. This way, the code testers see later in the SDLC becomes cleaner and easier to evaluate and improve. 

Benefits of Shift Left Testing

To make the case for testing code early and often, we must look at when bugs are most often introduced into code. In Capers Jones' often-cited book "Applied Software Measurement: Global Analysis of Productivity and Quality," the author claims that up to 85% of defects and bugs get introduced during the coding phase of development. 

If you're catching and fixing bugs early, your development team can reap numerous significant and measurable benefits. 

Cost Reduction 

When you can patch bugs during development, you make post-development software testing easier and faster instead of investing additional resources into stabilizing your code before deployment. 

In short, fixing bugs in earlier stages saves time and money. A 2018 Stripe study found that the average developer spends over 17 hours per week on tasks related to maintaining code, like debugging and refactoring. Developers also said that they spent four hours a week on average working on “bad code,” which, according to Stripe, equates to almost $85 billion in lost opportunity cost. 

A commonly cited analysis by the IBM Systems Sciences Institute claims that the cost of fixing a bug during implementation is six times greater than fixing bugs during design. The report also claims that fixing errors found after a product release costs four to five times more than fixing bugs uncovered during design and 100 times more than when bugs are identified during the maintenance phase. 

As the software progresses through the development cycle,  the cost of fixing bugs grows exponentially.

Improved Code Quality

Development teams are under growing pressure to deliver quickly. If you rush to push numerous fixes days before deployment, you’re now at risk of deploying, at best, a working but unstable product full of patches and, at worst, a faulty product. 

A 2022 report by Synopsys claims that poor software quality cost U.S. companies $2.41 trillion last year, up from $1.31 trillion in 2020. 

Code instability could also make future work and code expansions more difficult than they need to be. Another recent code study found that low-quality code takes, on average, 124% more time in development and that issue resolutions in low-quality code result in nine times longer maximum cycle times. 

The rush to deliver code quickly often leads to corner-cutting that can result in technical debt; the implied cost businesses take upon themselves when they don’t fix problems that will inherently affect them in the future.

One of shift left testing’s most significant perceived benefits is that it provides development teams with a process that enables them to increase production speed without sacrificing quality. 

Better Coverage

If you’re testing early and testing more often in the development process, it’s only logical that your test coverage stands to improve as well. With more people on your team performing tests during every stage of development, a larger portion of your application will undoubtedly be covered.

When applications are broadly tested for bugs, and a large percentage of your lines of code are executed under a test process, the number of issues appearing in later development stages should be minimal. 

In shift left software testing, documentation is vital to the coverage analysis process. When numerous people across various teams are involved in a continuous testing effort, it’s essential to keep clear records of the testing being performed. 

Proper test documentation of code coverage also helps your team prioritize testing application components that have potentially received the least attention throughout development. 

Challenges of Shift Left Testing 

Successful implementation of shift left software testing principles can’t occur if your team isn’t entirely on board with the process. The better your team understands the initiative and the more they’ve bought into its benefits, the smoother the transition. 

But, like with any adoption of new work models, getting shift left testing processes running poses some challenges.

Team leaders must create a clear transition plan so that everyone on the team knows what their new roles and expectations look like. Transitioning to shift left testing affects developers and QA testers the most, asking these teams to intertwine their work and collaborate more closely. 

When testing is no longer a linear and sequential effort that happens after development but a continuous process, constant communication and collaboration are required. 

Communication silos between teams must be eliminated. The tester’s point of view should be introduced into the process as soon as possible. Testers should be present and active participants in early planning and brainstorming sessions in which product features are discussed and design decisions are made. 

The most fertile development environment for implementing a shift left testing strategy is one in which developers know how to test and testers know how to code. They aren’t required to be experts, but programmers should know how to run automated tests, and testers should have enough coding experience to make quick fixes when minor errors and issues arise. 

When early testing processes are successfully implemented, your code becomes more testable over time, speeding up the testing process in all phases of the development cycle. 

How to Get Started With Shift Left Testing

How you implement shift left testing depends greatly on what your team looks like. Things like organization size and what your current processes look like certainly have a meaningful influence on how your team approaches shifting left. 

However, there are several key things to address that can get any team on the right track to shifting left.   

Define Coding Standards

Your testers should step in early to outline the level of code quality, security, and application performance that is expected. When coding standards are defined, your developers have an easier time learning how to test their code since they’ll know what types of errors and issues are unacceptable and need to be corrected.

With a defined agreement on coding standards, your team has a starting point for collaboration and getting everyone on the same page as you start to shift your development process left.

Identify the Right Tools 

If your developers don’t have a lot of experience testing, and many don’t, give them test automation tools that effectively aid the learning and implementation process. According to our 2024 State of Software Quality report, over 40% of teams still conduct unit and frontend testing manually. Since shift left testing is all about switching out ineffective manual testing methods for quick and continuous testing, it makes sense that various tools that can automate and speed up the testing process are essential. 

Static code analysis is a process that’s intrinsically tied to shift left. It’s the process of checking code as you create it—-running tests before executing the code. Static code analysis tools automate the process of checking your basic source code and ensuring that what you’re writing aligns with the coding standards your team has defined. 

Linters are a good example of a popular static code analyzer that can aid shift left testing tremendously. A linter compares your code with a predefined set of coding rules, checking for issues related to security vulnerabilities, syntax errors, style consistency, and more. If your code deviates from the rules your linter has been programmed to evaluate, the linter notifies you of any code issues that need fixing. 

When your developers use automated tools to evaluate code quality, they can catch and fix errors and issues through earlier testing, giving your tester cleaner and more manageable code to work with when they begin running their own more detailed and complex tests. 

Get Everyone Involved 

A shift left strategy can’t be implemented without close collaboration between developers and testing teams. However, it’s just as important to promote close cooperation across the entire team—project managers, business and data analysts, and designers—-to maximize the potential benefits of shift left testing. 

Work on integrating every key stakeholder into the process. When you can leverage every team member’s expertise, you can trim excessive operations and improve each project’s efficiency over time. 

By including non-technical team members, you’re also encouraging innovative and outside-the-box solutions by introducing new skill sets and unique perspectives and personalities to the software project. 

Shift Left Testing in Agile Development 

The shift left approach and Agile development are two concepts that can complement each other, as they share many guiding principles. Agile methodologies promote iterative and incremental development—working in small increments, allowing for early testing and feedback.

Both also emphasize continuous feedback and adaptation. As testing activities are performed early and often, teams regularly review and refine their work and make necessary adjustments promptly, based on the constant feedback between teams that shift left testing produces naturally.

Agile methodologies are inherently adaptable, as they prioritize responding to changes in team processes, customer needs, and market conditions. Early testing helps identify and respond to these changes more effectively.

Agile principles also emphasize collaboration and continuous communication within cross-functional teams. Reliance on test automation to move faster is also very important in Agile development, and Static Application Security Testing (SAST) tools are also essential to the testing tool stack of many teams that follow Agile methodologies.  

Shift Left vs. Shift Right Testing: What’s the Difference?

Shift left and shift right testing have a lot in common. They are both very Agile in nature, calling for incremental improvements through small and frequent builds. 

Let's think of the development cycle as an infinite continuum occurring from left to right in a constant loop. The left side focuses on the pre-production side of development, while the right side focuses on production—when the product is already available to users. 

The shift left testing approach allows teams to evaluate code quality and performance while the code is being created, speeding up development and reducing costs by finding and fixing defects before they get to production.

Shift right testing occurs in “real-world” conditions—when the product is released and already being used by customers. This late-stage testing ensures that your application is running in production and is meeting the demands and needs of the people who use it. 

In shift right testing, teams consider and remedy issues that are hard to anticipate or evaluate in the early stages of development, like application performance, reliability, and resilience. Some of the most common types of shift right testing processes include: 

• A/B testing in which you offer users two versions of new features, gathering customer feedback and measuring which solution customers prefer. 
  
  
• Chaos testing is when your engineers intentionally introduce errors and defects into your project to see how it reacts. These tests aren’t performed in “real-life” situations with customers but in a controlled, internal production environment. 
  
  
• Synthetic monitoring in which your team emulates paths users potentially take when engaging with your product. Automated tools used in this type of performance testing keep track of how your application performs and allow you to see and measure how typical user behavior affects the application’s performance. 

Both shift left and shift right testing prioritize incremental testing that allows you to “fail small and fail fast,” isolating issues in every development phase so that fixes can be made in pre and post-production in parallel and a continuous feedback loop can be established. 

Taking First Steps Towards Shifting Left 

Whether shift left testing is a good fit for you depends on your organization, your product, and your processes. However, shift left testing is a very flexible concept that just about any software development team should be able to implement to some degree. 

According to GitHub's 2022 developer survey, 57% of security team members said their companies have either shifted security left or planned on doing so over the course of the year. 

If you want to adopt shift left testing, a great way to get started is by trying out automated code quality and security testing tools that help you kick off the process of testing early and often in the development process. 

Codacy is an industry-leading test automation tool that’s used by hundreds of software teams to analyze billions of lines of code every day. To give our platform a try, sign up for a free trial via your GitHub, Bitbucket, or Google account.