Shift Left Testing: Why You Should Test Early, Test Often, and Shift Right Too
Understanding the “Shift Left” Mindset
Shift left testing means moving validation and quality checks earlier in the software development process. As Martin Fowler defines it:
Shift left is the process of taking a step that’s part of the value stream of software development and moving it up the timeline.
In practice, it often means shifting regression testing closer to the design and development phases, rather than waiting for a traditional QA cycle.
Visually, that’s simply doing this:
In a waterfall approach to software projects, testing has traditionally come after the code is complete, perhaps after a code freeze, and is the last step before the release.
The Real Cost of Finding Bugs Too Late
Catching bugs late in development gets expensive. According to James Martin, 56% of all defects come from the requirements phase, 27% from design, and 7% from coding (plus 10% other). IBM reports that fixing a security defect costs an average of $80 during development, $240 during build, $960 during QA/testing, and $7,600 after release. Another IBM study found fixing a bug post-release costs 30x more than fixing it during design. With most defects introduced early and costs skyrocketing later, shift left testing becomes a smart investment. 
Agile Alone Won’t Catch Every Bug
Agile helps by breaking releases into smaller, frequent chunks, but that alone isn’t enough. To shift left effectively, teams should use tests to drive development, even in short cycles. Early collaboration among users, designers, developers, and testers helps shape better outcomes. Turning requirements into test cases prompts stakeholders to think early about validation. Practices like test-driven development (TDD) or behavior-driven strategies support this shift.
When and Why to Automate Tests
To truly shift left, teams need to automate the tests that they create. Automation boosts test coverage by running more tests in parallel than manual efforts allow. It also frees testers from repetitive tasks so they can focus on higher-value work. Shifting left isn’t just about writing tests early—it’s about automating them. A full CI/CT/CD (continuous integration, testing, and delivery) pipeline helps run tests early and often while also streamlining deployments and reducing errors.
Thinking Beyond Testing
Although this post focuses on testing, the shift left mindset applies to more. Consider exploring shift left design and deployment strategies—both of which embed quality and collaboration from the start.
Don’t Forget About the Right Side of the Lifecycle
Defects become most expensive to fix after code hits production. One often-overlooked stakeholder? Operations. Shift right testing brings DevOps culture into play by focusing on what happens after deployment. Rather than “throwing the product over the wall,” shift right practices emphasize monitoring, observing, and analyzing production log data. This improves mean time to recover and reduces time to failure—metrics that help teams respond faster and improve continuously.
How Testing Fits into the DevOps Loop
Talking about shifting left and right shows that modern development isn’t linear. Software no longer follows a simple start-to-finish waterfall model. Agile teams now release functionality continuously in small, manageable updates. With continuous development and deployment comes the need for continuous testing. Dan Ashby visualizes how testing touches every phase of DevOps in this sketch.
Conclusion: Test Early, Test Often, Shift Smart
Shifting left and right can’t be plotted on a simple Gantt chart. Instead, they represent a continuous loop. Shifting left means embedding testing and automation throughout development. Shifting right focuses on feedback and performance in production.
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How can change management move from something organizations avoid at all costs to something they embrace? Similarly, how does testing turn from an afterthought into an essential part of reducing risk?
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