What is TDD– Test Driven Development

We recently published a post on how Business-Driven Development is helping businesses, technical teams, and developers to create useful business software.

Today, we’ll see how you can create a functional and effective product with Test-Driven-Development.

What is TDD (Test Driven Development)?

Test-Driven Development (TDD) is a software development technique in which software requirements are converted to test cases before fully developing the software. 

TDD tracks software development by testing the software against all test cases repeatedly.

Developed by U.S. software engineer Kent Beck, the development approach specifies and validates what a code will do by creating test cases. 

In other words, test cases are created for each functionality, after which they are tested. 

A new code is written if the test fails―the aim is to create a bug-free, simple code that will pass the test. 

To avoid code duplication, developers find TDD very instrumental in writing new codes when automated tests fail. 

The possibility of duplication is minimized as codes are written in small amounts to pass tests.

The TDD sequence is a unique software development technique, and in this article, we’ll find out what a TDD sequence is, its benefits, levels, test structure, as well as tools.

Table of Contents

1. The TDD sequence
2. TDD benefits
3. Scope of a TDD est
4. Comparing TDD with traditional testing
5. Levels of TDD
6. TDD Test Structure
7. Scaling TDD through Agile Model-Driven Development
8. Comparing TDD to AMDD
9. TDD Tools

The TDD Sequence

Test-Driven Development begins with the design and development of tests for each unit functionality of an application. 

TDD does not develop software before creating use cases. You can think of it as the opposite of an observation or study process. 

Instead of studying the system or feature, TDD seeks to create a feature that will play by its rules.

It creates requirements for a software system and stops at nothing till the codes created can implement the required system.

TDD is often called “Test First Development” because it operates on a test-first principle―developing and implementing automated tests before application development. 

Primarily, main Test Driven Development examples have to do with writing and correcting a failed test, writing a new code, then actual development.

In TDD, writing a test code is not an afterthought of writing a functional code. Instead, users write their test code before writing their functional code.

Also, this is done in tiny steps—taking a test and a small piece of corresponding functional code at a time. 

A programmer using the TDD approach doesn’t write a new function until a test fails because of that function’s absence. 

Practically, it sounds very simple, but using the TDD approach for the first time will require great discipline because it’s easy to make a mistake and write functional code first without writing a new test. 

This is a major advantage of pair programming as the user’s pair keeps them on track. A typical test-driven development example should follow the sequence below:

1. Create a Test

Integrating a new feature starts with writing a test that passes if and only if the product developed meets the specifications of the feature.

User stories and use cases can come in handy when a developer wants to gather information about the specifications.

Before going to execute a new feature, there’s a need to ask whether the current design is the best possible design that can allow the implementation of a functionality. 

If it is, then users can proceed with the Test First Development approach.

Focusing on requirements before writing the code remains one of the greatest pros of test-driven development. 

This opposes the conventional practice where codes are written before unit tests.

2. Run tests

When a new test fails, it should be for predictable reasons. This is proof that the automated test framework is functioning properly. 

It also corrects the impression that the new test has a problem and will pass all the time.

3. Write Some Code/Modify Existing Code

The code users write must be the most simple code that passes the new test. Hard coding may be allowed, provided the code passes the test. 

Hard coding in software development means embedding data into a program’s source code instead of generating it at runtime or externally. 

Hard codes will be removed during the refactoring stage. 

The system aims at avoiding code duplication at all costs and no code should be included beyond the functionality for which users the tests.

4. Every Test Should Pass

At this point, all the tests should pass. Where any fails, the developer must revise the new code till it passes. 

This makes sure that the code meets the test requirements and that already-present features are not compromised.

5. Refactor Where Necessary

The code is refactored to make it easy to maintain and enhance readability. Refactoring involves restructuring the already written code without altering its external behavior. 

Tests should be used after each refactors to make sure functionality is not compromised.

Users may refactor locally to change the part of the design that’s affected by a new feature. 

This allows them to add that feature as easily as possible to the system.

As a result, the quality of their design will keep improving, and this will lessen the amount of work they’ll need to put into related projects in the future.

As established earlier, all hard codes must be ousted during the refactor stage. Below are some of the activities included in the refactoring process:

• Deleting duplicate code
• Placing codes in their right locations
• Breaking processes into smaller units
• Making names self-describing
• Reordering inheritance hierarchies

6. Repeat the sequence

The above sequence is repeated for every new unit of functionality. The tests should be run in increments. 

This enables the programmer to undo or revert if the new code fails some tests. Like that, the programmer won’t have to do a lot of debugging.

Benefits of TDD

#1. Safer development

TDD is a system that makes continuous deployment safer. Test failures pause deployments and this allows the developer to fix any bugs before users notice them. 

In the database world, developers’ tests often comprise one-off scripts or manual tests. 

With TDD, users can establish a suite of automated tests over time and rerun them with other developers whenever they want. 

#2. Removes the Fear of Change

When changes that are made to the code introduce any bugs, the developer gets notified early. 

Once the bug is fixed, TDD’s tight feedback loop quickly alerts them, so that they remain in control of every development process.

#3. Produces simpler code, more flexible, and with superior design

TDD shows how the code will be used and its interactions with other modules. It results in more informed design decisions and code that can be easily maintained.

With test-driven development, codes are simpler to understand. This is because it favors the writing of smaller code with single responsibility instead of many procedures that have many responsibilities. The TDD process also ensures that user requirements are satisfied by writing only production code to pass the tests.

#4. Effective Teamwork

Teammates can confidently pick up the code and work on it in the absence of any team member. The exchange of knowledge between team members makes the team effective.

#5. It Favours Developers

Developing new features and debugging take less time in TDD.  

This makes up for the long time developers spend in writing test cases TDD also ensures less complicated and cleaner code.

#6. Quicker Feedback Loop for Developers

Conventionally, developers need to test every change to make sure that it’s functional. 

However, TDD automatically implements changes, giving faster feedback during development and debugging processes.

#7. Refactoring with Confidence

With a set of automated tests, breaks in the code used during refactoring can be fixed before release. 

The developer receives proper warning of breaks noticed when using automated tests, and the result is faster, more extensible code with minimal bugs and update risks.

#8. Obeys the KISS and YANGI Principles

KISS means “Keep it Simple, Stupid”, and YANGI means You Ain’t Gonna Need It”. These are two complementary software design principles. 

KISS advocates keeping the code and development processes simple.

YANGI advocates not building features if the features are not serving a particular existing requirement. 

TDD obeys these principles by making sure that codes are run in tiny iterations, fulfilling a requirement per time as the need arises. 

TDD says: If a feature is worth building, then it sure is worth testing. 

However, if it is not worth testing, then users shouldn’t waste their time working on it.

#9. Helps in Interface Design

The average development process prioritizes software implementation before the experience of the developer while using the software feature. 

This is a different story with TDD. It turns the process upside down, causing develo[ers to design the Application Programming Interface(API) before going into the implementation.

What Is The Scope of a TDD Test?

While running tests using TDD, the system must put the following into consideration:

• Boundary conditions
• Valid inputs
• Invalid Inputs
• Breaks in codes
• Exceptions, events, and errors.

Comparing TDD with Traditional Testing

The TDD approach is a specification technique that ensures thorough testing of a code to know if it passes a test to produce a functionality.

TDD is traditional development completely turned around. TDD and traditional testing are compared below:

• TDD focuses more on production code that proves whether testing will work well. However, traditional testing focuses on the test case design―whether or not the test will execute the application to produce a functionality.
• Unlike traditional testing, TDD allows its user to achieve a 100 percent coverage test. This is because every single line of code gets properly tested. 

The simplicity of the code makes its testing even more efficient. 100% coverage test is something that traditional testing recommends but doesn’t guarantee.

• A successful test finds one or more defects with traditional testing. This is the same thing with TDD. 
• When a test fails, users should know they’ve made progress because they now know there is a problem they need to tackle. 

Now they can predict that problem.

The more important thing is that there is even more success gained when the tests stop failing. 

TDD boosts confidence in the system―that it meets its defined requirements and that the user’s system works. 

This allows a user to confidently start working.

• TDD and traditional testing are not systems that strive for perfection. Instead, they make sure that the tests are consistent with the system requirements. 

Similar to TDD, traditional testing uses the risk profile of a system as the basis to determine how thorough the tests must be. 

This is consistent with Agile Modeling (AM) which advocates testing with a purpose and knowing why developers do the test and to what extent.

Though TDD is known as a specification technique, one may say that as a side effect, it produces more superior code testing than the traditional approach. 

What Are The Levels of TDD?

Test-driven development has two major levels that are every bit important to the whole process. These levels of TDD include:

1. Acceptance TDD (ATDD)

ATDD allows users to write a single test that satisfies the behavior of the system or fulfills the specified requirements. 

This is followed by writing a functionality or production code that is just enough to fulfill that acceptance test.

The acceptance test has to do with the total behavior of the system. Acceptance test-driven development was called Behaviour-Driven Development (BDD). 

Its code units usually implement a part of a requirement, so TDD tests can often be obtained from ATDD tests.

It is a tool used by the developer, customer, and tester to ensure that all system requirements are well-defined. 

It is usually readable by the customer and doesn’t require automation. 

1. Developer TDD (DTDD)

Developer TDD allows developers to write a unit developer test and just enough functionality code to fulfill that test. 

The single developer test focuses on all of the system’s small functionalities, one after the other.

Developer TDD is also called TDD. Both TDD and ATDD serve the same purpose―which is to specify detailed and executable requirements for Test-driven functionality on a just-in-time (JIT) basis. 

JIIT increases efficiency by taking only the requirements that are needed in the system. 

Test automation is a requirement in TDD. Also, customers should not read TDD tests.

TDD Test Structure

Properly laying out a test case helps users to complete all required actions, increases the readability of the test case, and makes execution more efficient. 

To build a self-documenting test case, a consistent structure is required. Here is a commonly used structure for test cases:

• Setup: The Unit Under Test(UUT) or the whole test system gets placed in the right state necessary for running the test.
• Execution: This involves driving or triggering the unit under test to produce the required behavior and include all output like output parameters and return values. This is usually a simple step.
• Validation: there is a need to ensure that the test results are correct. Such results may include state changes in the unit under test or specific outputs captured in the execution stage.
• Cleanup: The overall system or the unit under test gets restored to its pre-test condition. 

This allows execution of other tests immediately after the former one.

Sometimes, to save information for test failure analysis, beginning the test before its setup run should be the cleanup.

Scaling TDD through Agile Model-Driven Development (AMDD)

TDD thrives at providing a detailed specification and validation of software requirements. 

However, it hardly thinks through bigger things like UI, use of the system, or overall design.

AMDD caters to those Agile scaling issues that can’t be resolved using TDD. That is why AMDD is used to solve bigger software issues.

AMDD Lifecycle

Model-driven development (MDD) involves creating extensive models before writing the source code, and this follows an agile approach.

Predicting the tests which will be run during the first week of the development project is called envisioning. The major idea behind envisioning is to determine the scope and architecture of the system.

Architecture modeling and high-level requirements are usually done for successful envisioning. 

It is a process where developers do a non-detailed software specification by exploring the software requirements that define the project’s overall test strategy.

1. Envisioning

The envisioning stage involves the following:

• Envisioning Initial Requirements

The goal is to explore user interface (UI), usage, and Initial domain models. Identifying high-level requirements could take up to several days.

•  Envisioning Architectural Requirements

The goal here is to explore Change cases, technology diagrams, domain models, and UI flow. It provides technical insight for the project and could take several days.

2. Iteration Modeling

This involves the team taking time to plan or model what must be done in each iteration.

• Each iteration uses an agile process. That means a new work item is added to the system with priority during each iteration.
• The ,ost prioritized work item will first be taken into consideration. After that, added work items may be readded or removed from items stack at will.
• The team goes through how each requirement will be executed. This is where modeling comes in handy.
• Each requirement that will be implemented for that iteration passes through modeling analysis and design.

3. Just in Time (JIT) Modeling

People also refer to this as Model Storming.

• A team of 2 or 3 members starts a modeling session, discussing issues on a whiteboard, paper, or monitor.
• A team member asks another to model with them. The process could take up to 10 minutes when the team shares the paper or whiteboard between themselves.
• They go through issues until they can’t find the major cause of the problem. If, just in time, a team member sees an issue which they want to be resolved, they can request help from other team members.
• The other teammates explore the issue, and everyone continues the process as before. It’s also known as customer QA sessions or stand-up modeling.

4. TDD (Test Driven Development)

• It enhances detailed specification and confirmatory testing of the application code used.
• Detailed requirements (acceptance test) and unit tests (developer tests) are both TDD inputs.
• With TDD, users can write clearer and simpler code; it reduces the size of developers’ documentation.

5. Reviews

This has to do with inspecting codes and reviewing models. It is an optional process and can be done either for the whole project or each iteration. It helps to provide feedback for the project.

Comparing TDD (Test Driven Development) to AMDD (Agile Model-Driven Development)

TDD (Test-Driven Development)	AMDD (Agile Model-Driven Development)
TDD gives a detailed specification of system requirements.	AMDD is more suited for issues like UI, system use, and overall design.
TDD helps to shorten the programming feedback loop	AMDD helps in shortening the modeling feedback loop.
TDD communicates better to programmers.	AMDD communicates to data professionals, stakeholders, and business analysts.
TDD enhances high-quality code development.	AMDD promotes world-class communication with developers and stakeholders.
TDD does not have a visual orientation.	AMDD does not have a visual orientation.
TDD and AMDD both support evolutionary.	AMDD incremental software development.
TDD pays little attention to software works	ATDD provides a better platform for every team member to understand the project.

What is TDD Tool?

To fully utilize Test Driven Development, there are some important tools that users and developers can apply. 

Below is a list of some tools developers can use for TDD;

• VBUnit
• xUnit.net
• XTUnit
• csUnit (.Net)
• cpputexst
• CUnit
• DBFit
• DUnit (Delphi)
• DBFit
• Do test(Python)
• JUnit
• Moq
• JMock
• HTMLUnit
• PHPUnit
• Google test
• HTTPUnit
• Test::Unit (Ruby)
• TestOoB (Python)
• PyUnit (Python)
• OUnit
• Test NG
• NUnit
• NDbUnit
• Simple Test

Conclusion

We’ve shared a complete guide on “what is TDD?” and Test Driven Development examples. Here’s a redcap:

Test-Driven Development prioritizes testing a code’s ability to produce a functionality by creating test cases for the functionality.

It turns the scientific approach of just observing or studying a system upside down. 

Instead, it allows the developer to create any functionality they desire and bring it to life after passing the required tests.

As a major advantage, Test Driven Development helps developers to write simpler code and implement features unit by unit. 

It follows the KISS and YANGI principles that advocate keeping code simple and integrating the most necessary features; this reduces the amount of code the programmer processes and makes development more fun and interactive. 

A hybrid of TDD and AMDD has greatly improved the capabilities, and the number of developers using TDD continues to increase.