What Is Test Driven Development (TDD)

Three Phases of Test Driven Development

The Test Driven Development (TDD) process comprises three basic steps: writing the test first, writing the code to pass the test, and then refactoring the code.

Let's take a closer look at each of these steps.

Writing the test first (Red Phase)

The first step in the TDD process is to write a test that verifies the code's behavior. This test is written before the actual code is written and must fail before the code is written. This ensures that the test is valid and tests the correct behavior.

When writing a test, it is important to keep it as simple as possible. Tests should be written to verify one specific piece of functionality, and each test should be independent of other tests. This helps to ensure that the tests are easy to understand and modify.

Make the Test Pass (Green Phase)

Once the test is written, the next step is to write the code that passes the test. This code should be written to pass the test and nothing more. This helps ensure that the code is focused on the specific functionality being tested and is not overly complex.

When writing the code, it is important to keep it as simple as possible. The code should be easy to understand, and it should not include any unnecessary complexity. This ensures the code is maintainable over time.

Refactor the Code (Refactor Phase)

The final step in the TDD process is to refactor the code and improve its design. This is a crucial step as it ensures that the code is maintainable over time and that it is easy to modify and extend.

When refactoring the code, it is important to keep the tests passing at all times. This ensures the code is still working as intended and that any changes to the codebase do not break existing functionality.

How Test Driven Development (TDD) Work?

We will look at the working of the three phases in detail by understanding it using a flowchart.

• Write a Test (Red Phase): Create a test focusing on a small feature you want to add. It should also be written so that, at first, it fails because the feature has yet to be available. Since the test is predicted to fail at this point, it is called a "failing test" or the red phase.
• Execute the Tests (Red Phase): Run the test that you have written. The test will fail since you still need to build the functionality, which is the anticipated outcome.
• Write Minimum Required Code (Green Phase): After setting up a failed test, you write the minimum code needed to pass the test. This indicates that your goal should be to design a solution that satisfies the test case rather than flawless or feature-rich. The objective is to pass the test and change its status from "red" to "green."
• Executes the Tests (Green Phase): You run the test once the code has been written. If it passes, the test case will be satisfied because you have successfully built the bare minimum of functionality.
• Refactor Code (Blue Phase): After the test passes, you can refactor your code to make it more optimized, readable, and effective. Here, you must test the code again, as it assures you that your changes won't result in new bugs. Once your tests run successfully, you can implement these improvements without worrying that you'll damage current functionality.
• Repeat: This cycle is continued by writing new test cases, writing the bare minimum of code required to pass them, and reworking as required. Each test case enhances the codebase and adds a tiny amount of functionality. This iterative approach continues until you've finished implementing the feature or reached the desired level of coverage.

Here is a code example of how Test Driven Development (TDD) works:

Suppose you want to implement a function that adds two numbers together.

You would start by writing a test for the below function (Red Phase):

public class TddExample {
	@Test
	public void testAddTwoNumbers() {
    	assertEquals(3, addTwoNumbers(1, 2));
	}
}

Running this test would fail because the add_two_numbers() function doesn't exist yet.

Next, you would write the minimal amount of code to make the test pass (Green Phase):

̧public static int addTwoNumbers(int a, int b) {
	return a + b;
}

Running the test again would now pass.

Finally, you would refactor the code to improve it without changing its functionality. For example, you might remove the useless return statement (Blue Phase):

̧public static int addTwoNumbers(int a, int b) {
	a + b;
}

You can proceed to the following functionality if satisfied with the code.

Best Practices in Test Driven Development (TDD)

Following best practices to get the most out of Test Driven Development (TDD) is important.

• It is important to ensure that the development team understands TDD. Because sometimes writing the test can require more effort than writing code.
• Some of the best practices include writing tests that are simple and easy to understand, writing code focused on the specific functionality being tested, and refactoring the code to improve its design and maintainability.
• Run all the tests as part of the development pipeline. So that any failing test case stops an executing pipeline
• It is also important to use tools that support TDD, such as unit testing frameworks, code coverage tools, and continuous integration tools. These tools can help to automate the testing process and make it easier to catch bugs early in the development process.
• Finally, it is important to ensure that the entire team is on board with TDD. This includes developers, testers, and project managers. By working together to implement TDD, teams can improve the quality of the codebase, reduce the overall cost of software development, and ensure project success.

Common Mistakes in Test Driven Development (TDD)

While Test Driven Development is a powerful technique for software development, there are some common pitfalls that developers should know.

• One of the most common pitfalls is writing tests that are too complex or that test too much functionality at once. This can make the tests difficult to understand and modify over time.
• Writing code that is overly complex or that is difficult to understand. This can make it challenging to maintain the code over time and lead to technical debt in the codebase.
• It is important to ensure that the tests are testing the correct behavior. If the tests are not testing the correct behavior, then the code will not work as intended, and bugs can be introduced into the codebase.
• TDD is not meant to provide complete functional testing. Independent integration testing and compliance testing will be required.
• For a successful Test Driven Development implementation, requirements should be very clear and understood by the developer. Only then it is possible to write correct test cases, and the entire development depends on what test scenarios we cover. Otherwise, unit testing might not be effective.
• In a high-complexity project, Test Driven Development can considerably increase the project's cost. Because running a complex project will require many test cases, and implementation of a large number of tests can take time.
• A poorly maintained test suite could also cause many performance issues. A lot of times, tests become part of the maintenance overhead, and inefficient written tests can further raise maintenance costs.
• Writing too many test cases or too many trivial test cases is also one of the pitfalls.

Some Common Myths about Test Driven Development (TDD)

As for other development strategies, few myths and conceptions are dwelling while TDD is put to use. Below are a few myths that need attention.

Myth 1: TDD Is the same as unit testing.

Reality: TDD is not unit testing. An experience in creating unit tests does not mean that we’ve applied Test Driven Development. TDD is not about writing unit tests. It is an approach to writing production code that happens to produce unit tests that follow the rules and a cycle of steps.

Myth 2: With TDD, all the tests are written before the production code.

Reality: TDD does not ask you to write every test and then start on your production code. It involves writing a single test that fails and then just adding enough code necessary to make the failing test pass. We add tests to your codebase just as we do it for production code but here incrementally.

Myth 3: TDD Practitioners do not consider creating or thinking about design or architecture.

Reality: Test Driven Development is, again, a sequence by which we keep refactoring code. This absolutely does not restrict us to not think through the design, looking out for pitfalls, or creating whiteboarding architecture. Irrespective of whether being in TDD or not, these are integral parts of the development process.

Myth 4: TDD is a test strategy and can potentially replace QA.

Reality: This, just like all the other myths, is a fundamental misconception about the nature of TDD. The term “Test Driven Development” echoes development! So, eventually, It is a development technique and not a QA approach. The TDD method involves breaking the code into small functionality components and defining "done" before moving on to the next incremental piece. Write a test that fails, but you know that when it passes, you’ll be done with the current piece you’re working on. It does not include smoke tests, regression, or load tests. No, it can never swap for a QA job.

Myth 5: Test Driven Development slows teams down

Reality: At the start, when TDD is put to use, the development team might feel it is slowing down the development process, but if we think of it this way if a feature needs an hour to develop, but we spend 6 hours debugging the errors, is even more time consuming than spending 6 hours developing the feature through TDD and need no time debugging it.

Myth 6: The goal of Test Driven Development is 100% test coverage.

Reality: Since TDD is a development methodology, it does not aim to achieve testing strategy goals. The goal is to have a code that is easy to refactor, well-understood, maintained, and with its behavior specified.

Is Unit Testing a part of TDD?

Unit testing has been there since the inception of programming. However, the methods of unit testing have evolved over the years. TDD is about writing the test code before writing the production code.

So, what is the difference between unit testing and TDD? Unit testing is creating tests for the already written code, unlike TDD. Unit testing focuses on unit functionality, while TDD also focuses on design and testability. However, with TDD, we also write unit test methods. And that is how unit testing becomes a part of Test Driven Development.

Unit testing is an integral part of TDD. Although some teams may be hesitant to forgo traditional unit testing, TDD drives code development, and every line of code has a corresponding test case. This means that unit testing is already built into the practice. Unit testing is performed in a loop on the code until requirements are met. This eliminates the need for additional unit test cases.

There have been several case studies that have found that built-in unit testing leads to better code. In one of the case studies for a project, some team members used TDD while others wrote unit tests after the code was complete. To a surprise, TDD coders had finished and produced more reliable code than the developers who wrote unit tests.

In comparison to TDD, which drives entire application development, unit testing only tests functions, classes, and procedures.

To fully benefit from unit testing and TDD, automated unit test tools should be used to automate tests. Automating tests is critical for continuous integration and is the first step in creating an automated continuous delivery pipeline.

So, when to use TDD and when to use unit testing?

Unit testing and TDD both minimize bugs in the code. TDD is a design process that helps to achieve cleaner code with high coding standards. So, it is best to use TDD when it is a new project. Unit testing is like a passive form of testing. It does not actively modify the code to see if it works. So, it is always an advantage to use unit testing for an existing codebase to test. For a developer with prior experience with unit testing, TDD is a boon.

There are a few situations when unit tests are better than TDD.

• When the existing code is complex, it is difficult to write a test first and then code.
• Using mocking frameworks to create stubs and mock objects for the class under test and writing test methods isn't always beneficial.
• Although TDD aims to achieve maximum code coverage for a complex project, it is good to start refactoring code with the unit test results and then include TDD.

Acceptance TDD and Developer TDD and Behavior-Driven Development

Testing practices are critical for any organization and project implementation. Several testing practices promote the quality of software products. Below we will explore a few test strategies that would help us widen our scope beyond TDD.

ATDD or Acceptance Test Driven Development

Acceptance Test Driven Development involves creating a single acceptance test that meets the requirements of the system's specification or behavior. Once the test is in place, the developer writes only the necessary production or functionality code to satisfy that test. The acceptance test evaluates the system's overall behavior and is sometimes referred to as Behavioral-Driven Development (BDD).

It focuses on test automation. It is extended on the TDD approach to improving the collaboration between developers, testers, and business participants. It is also frequently related to Agile methodologies.

In this, the tests are written from the user's perspective, and like TDD, test cases are written before the actual coding begins.

Some advantages of using ATDD are:

• It helps prioritize customer needs.
• The development takes place in small iterations, so it is easy to manage.
• It enables the developers to identify and resolve issues quickly.
• It fosters improved collaboration between product owners, developers, testers, business analysts, and cross-team members.

TDD or Developer Test Driven Development

Test Driven Development involves writing a single developer test, typically a unit test, and then creating just enough production code to pass that test. These unit tests focus on each small aspect of the system's functionality. Developer TDD is often referred to as TDD.

Both Acceptance TDD and Developer TDD aims to specify detailed and executable requirements for the solution on a just-in-time (JIT) basis. JIT involves considering only the requirements necessary for the system, resulting in increased efficiency.

Some advantages of using Developer TDD are:

• Reduces rework
• Identifies bugs or errors quickly
• Feedback is fast and therefore encourages the development of neat and clean web designs.
• Any team member can start working on the code without dependency on a specific team member. This promotes knowledge-sharing, collaboration, and trust.
• The ability to refactor allows the creation of flexible and maintainable code.

Behavior-Driven Development (BDD)

Behavior-Driven Development is a testing approach derived from the TDD methodology. In BDD, the tests are mainly based on the system's behavior-hence its name. In most cases, the Given-When-Then approach is used for writing test cases.

Consider a scenario where the user is trying to login.

• Given: The user entered valid login credentials.
• When: That user clicks on the login button.
• Then: Display a successful validation message indicating he could login.

In the ATDD technique, a single acceptance test is written from the user’s perspective, mainly focusing on satisfying the system’s functional behavior. This technique expects to answer the question – Is the code working fine?

So, ATDD might sound very similar to BDD. However, a key difference between them is: BDD focuses more on the behavior of the feature, whereas ATDD focuses on fulfilling the requirements. Also, ATDD and BDD use simple English words to describe a test case.

Few advantages of using BDD are:

• The use of a simple English language helps reach a wider audience.
• Emphasize how the system behaves from the customer’s and the developer’s perspective.
• Compared to other techniques, the implementation of BDD is a cost-effective technique.
• Minimizes post-deployment defects

But it’s not always about ATDD vs. BDD vs. TDD. It is about how we make them work together. It is not always necessary to select between them and use one specific technique. Based on the project’s requirements, we can combine any to gain the maximum advantage.

Role of Test Coverage in TDD

Test coverage is the percentage of code that tests cover to ensure that the code is thoroughly tested and that any potential bugs are caught early in the development process.

To achieve high test coverage, it is important to write tests that verify the code's behavior and cover all possible code paths. This helps to ensure that the code is working as intended and that any changes to the codebase do not break existing functionality.

It is also important to use code coverage tools to measure the test coverage and identify codebase areas uncovered by tests. This helps to ensure that the code is thoroughly tested and that any potential bugs are caught early in the development process.

Conclusion

Test Driven Development is a powerful development practice that has become increasingly popular in recent years. By writing tests first and then developing code to meet those tests, TDD enables developers to create more robust and reliable software while reducing the time spent debugging and fixing issues. TDD encourages a focus on small, testable code units and promotes collaboration and communication among team members.

TDD requires a shift in mindset, just like in Agile, so whether you are a beginner or an experienced developer, TDD is a valuable practice for any development team looking to improve and produce more reliable code and products. So, get ready to take your software development skills to the next level with Test Driven Development.