Test driven development (TDD) is a development process in which tests are written for a new piece of code before the code is written. The tests describe the desired behavior of the code and serve as a guide for its implementation.

The process of TDD usually involves the following steps:

1. Write a test that defines a small piece of desired functionality.

2. Run the test and see it fail, since the code to make it pass does not yet exist.

3. Write the minimum amount of code necessary to make the test pass.

4. Run the test and see it pass.

5. Refactor the code to make it clean and maintainable, while ensuring that the tests continue to pass.

TDD is designed to encourage the creation of high-quality, well-designed code by ensuring that all code is tested and that tests are written before the code is implemented. It can also help developers to think more carefully about the design and functionality of their code, as they must consider how the code will be tested before they write it.

The Pros of Test Driven Development

Test-driven development (TDD) has several benefits:

1. Improved code quality: By writing tests before writing the code, developers can ensure that their code is well-designed and meets the desired functional requirements. This can lead to higher-quality code that is less prone to defects.

2. Faster development: By writing tests before writing the code, developers can focus on one small piece of functionality at a time, which can make the development process faster and more efficient.

3. Easier debugging: If a test fails, it is easier to identify the source of the problem because the tests are written before the code. This can save time and effort compared to debugging code that has not been tested.

4. Greater confidence in code: By continuously running tests as the code is developed, developers can have greater confidence in the functionality and reliability of their code.

5. Better documentation: The tests written during TDD can serve as documentation for the intended behavior of the code, which can be helpful for other developers working on the project or for future maintenance.

6. Better communication: By writing tests before writing the code, developers can clearly communicate the desired functionality to the rest of the team and stakeholders, which can improve collaboration and reduce misunderstandings.

The Cons of Test Driven Development

Test-driven development (TDD) is a widely-used and effective software development process, but it is not without its limitations. Some potential drawbacks to TDD include:

1. Additional time and effort: Writing tests before writing the code requires additional time and effort upfront. This can be particularly burdensome for projects with tight deadlines or limited resources.

2. Difficulty with legacy code: TDD is most effective when it is used from the beginning of a project. It can be more difficult to apply TDD to legacy code that was not developed using this process.

3. Requires discipline: TDD requires discipline and commitment from developers to follow the process consistently. If developers are not diligent about writing tests before writing the code, the benefits of TDD may not be realized.

4. Limited to testing the expected: TDD is focused on testing the expected behavior of the code, which means it may not be effective at identifying unexpected or edge case behaviors.

5. Not always suitable: TDD may not be suitable for all types of projects or for all developers. Some projects or developers may find other methods, such as behavior-driven development or exploratory testing, more effective.

How Test Driven Development Fits with Agile

Test-driven development (TDD) is a software development process that can be used in the context of an agile software development approach. In agile development, the focus is on delivering small, incremental changes to a project quickly and iteratively.

TDD is well-suited to the agile development process because it encourages the creation of small, modular pieces of code that can be tested and delivered incrementally. By writing tests before writing the code, developers can ensure that each small piece of functionality meets the desired requirements and can be delivered quickly and reliably.

In an agile development environment, TDD can be integrated into the development process as follows:

1. During the planning phase, the development team identifies the functional requirements for a new feature or change to the project.

2. The team writes tests that define the expected behavior of the new feature or change.

3. The developers write the minimum amount of code necessary to make the tests pass.

4. The tests are run to ensure that the code meets the desired functionality.

5. The code is refactored to ensure that it is clean, maintainable, and follows best practices.

By following this process, the development team can quickly deliver small, high-quality changes to the project that are well-tested and reliable.