Test-Driven Development (TDD): How Does it Help in Software Development

No matter where you are in a software company, you’ll know that quality code is essential to a successful product and satisfied customers.

Good developers have a craftsman’s mindset to their work. You’ll feel the improvement in the whole team’s morale if they know they’re writing great code that’s free of bugs and complications. To utilize time, the time that they’re not spending on debugging, can be spent polishing the product to perfection.

Many SaaS companies use practices like user stories or empathy maps to improve customer experience. However, the customer experience can be improved long before they even see the product by simply ensuring that your code is of high quality.

Everyone wishes they could write error-free code the first time. While that may be a pipe dream, we have to find ways to get as close to that as we can. The stakes are high as bugs are one of the quickest ways to frustrate users and convince them to look at your competitors. If you’re in a B2B company, that very one customer could be one of your all-important key accounts.

Test-driven development won’t prevent bugs, but it will make sure you catch them long before a user does. Not only that, but it also has all kinds of secondary benefits that’ll save you time and money.



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What is test-driven development?

“Test-driven development” is a term coined by Kent Beck in 2003. The trick is to break your code down into the smallest pieces you can before you put them into production. You write a “test plan” specifying each piece’s inputs and expected outputs, then branch into an iterative process until the whole product has been completed.

This saves your developers valuable time writing long stretches of code, thaen having to spend most of an afternoon combing through it to find the inevitable bug. You get to inspect each unit of code like it’s one part of an engine. If every piece works as expected, the car will run. If one piece is broken, you’ll spot it before it gets into the machine.

The benefits of test-driven development

Benefits of the test-driven development cycle includes:

  • Better communication across teams as people have to think clearly about what each part of the code requires.
  • Among other agile benefits, test-driven development enables teams to catch bugs faster. Because testing is so thorough and incremental, it’s easy to do automated regression testing, which catches new bugs when they appear in code.
  • Less time debugging, more time on valuable and innovative work.
  • More modular, readable, extensible code that will make sense to new hires years from now.


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The test-driven development cycle

The test-driven development cycle has six main steps, which you’ll run in a repeating loop until the whole product is ready to ship.

1. Create a test

You don’t start writing a feature until you have a test plan. A basic test plan could fit on a post-it note – . You just need to list inputs and expected outputs. This forces you to think clearly about what the feature requires and explicitly make any assumptions, which is a great habit for a whole team to get into.

2. Run all of the tests

The second stage requires the running of a test case execution. You’ll run your freshly-added test here on its own, as well as the whole battery of tests you’ve written before. This ensures that your new test works and that your new code hasn’t altered the output of any of your other code or broken it entirely. Although your tests are separated, they might have to talk to each other to resemble your finished product.

3. Write just enough code to pass every test

You’ll know that every new line of code is a chance for a new bug to appear, which is why you should only write enough code to pass the whole battery of tests before you start adding extra features.

If necessary, one way to ‘“cheat’” at a round of testing is to have one block of code return its expected output as a hard-coded value. If you know “returnTotal” needs to output a price for the program to work, you can just write for example, “return ‘$20.50’” so that it enables you to test everything else that relies on it.

In a time-pressure situation like an innovation challenge or a design sprint, developers can test thoroughly without getting bogged down on one tiny issue.


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4. Repeat step three

Run all your tests again, and if something fails, go back to step three. If your software has passed all the tests it needs to, it’s ready to get reviewed and merged into the production code.

5. Refactor

One common mistake innovative companies make under pressure is doing the quick solution that works rather than the most “correct” one. Over time, it’s necessary to review and refine old code to keep the product running efficiently. This could be laborious, but if the old code was built by test-driven development, you’d still have the battery of automated tests lying around.

As developers tweak the old code, they can quickly run the automated tests to ensure they haven’t broken anything and safely send the Pull Request.


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6. Repeat steps one-six

Test-driven development is great for thoroughly testing early-stage software. However, it’s useful throughout the whole product lifecycle. As the product matures, you can keep cycling through this process every time you add a new feature to make sure nothing causes a “regression”, i.e., a new bug that wasn’t there in the last version released to your customers.

How test-driven development can help in software development

Test-driven development has many positive effects beyond just reducing bugs.

Code is more modular

Because of the focus on small unit-testing, the process lends itself to more modular code, which is broken up into small, easy-to-manage pieces.

In something complex like retail management software, this is extremely important as millions of dollars might rest on several hundred interlocking parts working flawlessly every time. With each addition to the product, the likelihood of a bug increases exponentially, making it essential to implement test-driven development early while the product is still small.

Easier maintenance

This clear, modular, well-organized code is easy to maintain. It’s simple and convenient, such that only a few comments are needed in the code for readers to understand what it’s doing.

This is good for the product and the company as a whole because developers can come in and easily understand mission-critical code that was written years ago. This is essential for easy debugging as well as rapid additions to the product.

Easy refactoring

Refactoring code is much easier with test-driven development. This goes for code that was built in a test-driven way, as well as old code that’s being rewritten to comply with new testing standards.

All of the benefits of the process apply to the rewriting of code as well as initial development. Developers can write their test plans for the existing code, rewrite to the new standards that need to be met, and confidently run a battery of automated tests to make sure nothing in the old code has been broken.

Where crowd testing ecommerce solutions like A/B testing require vast audience data to catch regressions due to refactoring, test-driven development protects companies from shipping those bugs at all.

As Steve Jobs used to say of Apple, “We don’t ship science projects”. With test-driven development, your company doesn’t have to ship science projects either.


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Reduced costs

Test-driven development will cost more time, money, and effort in the short term than traditional development cycles. However, as with any other investment, your team needs to track savings over the whole lifespan of the software, just as with your marketing team’s KPIs for affiliate marketing or the hours the sales team spends talking to potential key accounts.

If automated testing isn’t built out early in the product’s life, it’s going to be even more expensive down the line when a buggy product forces the team to build those capabilities all at once. By applying test-driven development early in the product’s life, you’ll have a manageable testing suite that grows naturally with the product and doesn’t require a costly team effort to build.

Self-documenting code

Test-driven development allows for better observability in software engineering in a number of ways, but the clearest is perhaps the improved documentation.

You can save hours writing special documentation explaining how the software works because the code is self-documenting. This is the gold standard of software development, and with testing, you can get closer to this easy-to-read code with every new feature your team builds.

The power of test-driven development

Test-driven development helps you write better software and ship better products. It requires some investment of time and effort upfront. However, as the product moves towards completion, you’ll see the benefits of clear, error-free code that doesn’t have to be debugged at the last minute.

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