Test Driven Development

Test-Driven Development (TDD) and why you should care.

Test-driven development is a progressive, incremental approach to software development.

Some key fundamentals about TDD which may improve the quality of your software.

Why Use TDD?

Test-Driven Development(TDD) is often preferred especially for large projects rather than the traditional Test-Last Development (TLD) process due to very efficient benefits that it can provide.

Some advantages of using TDD:

Reduces Dependence on Debugging

For TDD, a unit is most commonly defined as a class, or a group of related functions often called a module. Keeping units relatively small reduces debugging effort. When test failures are detected, having smaller units aids in tracking down errors.

In TDD, it’s important to test one function in a single test. Have specific tests created for each bug in the program. These tests will automatically run when there is another bug fix, making sure that bugs will not reoccur in the code.

Saves Cost and Time

Writing the tests firsts makes developers consider the objectives and requirements of the code they need to craft firsthand. This allows them to create a more detailed specification straightaway.

With TDD, tests are automated, and it saves a lot of time while ensuring good code quality compared to manually testing functionality. Because tests are in place up front, time allocated for regression testing can be reduced considerably which eventually reduces the costs of finishing a program.

Improves Code Quality

Small test cases are easier to read and to understand. TDD allows developers to create a full set of tests that will let you know if anything breaks so you can fearlessly refactor your code leading to better code readability and maintainability.

TDD leads to improved design qualities in the code, for instance improving the metrics of cohesion and coupling. It also helps keep the code as simple as possible.

TDD is often preferred for its ability to detect bugs accurately and to provide insight into the current state and behaviour of the program. It presents a code base as a set of small, modular, composable units. This makes refactoring and/or adding new features much easier thus helps to improve its flexibility, adaptability and the overall code quality.

Test-Driven Development Cycle

TDD Cycle is also known as the RED-GREEN-REFACTOR CYCLE: is when a developer writes a failing automated test case, then produces the simplest code needed to pass that test, refactors the code until it meets acceptable standards.

Steps used in TDD

Add a test

Write a single unit test that succinctly defines a function or improvements of a function. Understand the feature’s specification and requirements to write the test in a testing framework suitable to the software environment.

This could be a modified version of an existing test. The TDD approach makes the developer focus on the requirements before writing the code unlike writing unit tests after the code is written.

Run all tests and see if the new test fails

TDD validates that the test harness is working correctly and shows that the new test does not pass without requiring new code because the required function already exists. It eliminates the possibility that the new test is flawed and will always pass. The new test should fail for the expected reason.

Write the code

Write code that is just enough to cause the test to pass. Keep the code as simple as possible. It does not have to be the most perfect piece of code as long as it can solve the initially failing test.

Do not write code beyond the functionality that the test checks or requires.

Run tests

Run and re-run all tests until all cases pass to ensure that the newly added code meets the test requirement without breaking functionality or degrading any features.

If tests cases do not pass, the new code must be optimized until they do.

Write tests with minimum code changes after every test runs to ensure that good unit tests coverage for the software will eventually add up to the overall quality of the product.

Refactor code

Refactoring is a crucial step between each pass and every next failure.

Refactoring is essential to make sure that the code conforms to the simplicity criteria while it maintains functionality. Move the new code from where it was convenient for passing a test to where it more logically belongs to keep your code neat and agile.

Remove duplication and aim to improve the software’s readability and maintainability.

Continually re-run the test cases throughout each refactoring phase to ensure that the process will not alter any existing functionality or to confirm that there are no additional bugs that have been introduced.


Repeat the cycle for continuous integration pushing functionality forward.

Have as few as 1 to 10 edits between each test run and keep the size of the steps small. This is to easily undo or revert the code if it does not instantly satisfy the new test, or other tests fail unexpectedly.

It will help reduce the need for debugging in the later parts of the development cycle.

If you’re not applying TDD perhaps it’s time to give it a go it might just help improve the quality of your software and reduce time spent in maintenance.

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