As you prepare for the Advanced Certified Scrum Developer (A-CSD) exam, one essential studying area is Test-Driven Development (TDD). TDD is a software development approach in which test cases are developed to specify and validate what the code will do. In the TDD context, we adhere to three guiding principles: Red, Green, Refactor.
1. Red: Write a failing test.
This principle encourages developers to first document what they want the software to do, by scripting a small test case before writing any production code. Every test targets a tiny portion of the application’s requirements. In other words, the test is designed to fail because the function or feature it tests isn’t implemented yet. This guiding principle of ‘Red’ is fundamental because it:
- a. Ensures that the requirement is well-understood before the code is implemented.
- b. Verifies the test is correctly designed and passing for the right reasons.
- c. Facilitates early error detection. The tests will provide immediate feedback if the newly written code does not meet the requirements.
For example, let’s say we are developing a program that calculates the sum of two integers. The test case should be written and fail first before implementing the actual function. Imagine it in Python code:
def test_add():
assert add(1, 2) == 3
Here, add is the function to be implemented. When this test is run, it will fail because add doesn’t exist yet, satisfying the ‘Red’ stage in the TDD cycle.
2. Green: Make the test pass.
The green phase of TDD involves writing just enough code to get the designed tests to pass. Avoid the temptation to write more functionality than the tests cover at this stage. The disciplined way to adhere to ‘Green’ in TDD is :
- a. Write merely enough code to pass the test.
- b. Avoid the anticipation of upcoming requirements.
Adhering to ‘Green’:
- a. Prevents over-engineering. Consequently, the codebase remains neat and clean, with no dead code.
- b. Enhances software maintainability because every piece of code written is needed and verified by a test.
Following the previous example, the implementation to make the test pass in Python could look like this:
def add(x, y):
return x+y
Even if we already know that the function would need to include input validation (e.g., checking if x and y are integers), we should not add this piece of functionality yet because there isn’t a test that covers the requirement.
3. Refactor: Remove duplication.
The final phase simply involves cleaning up the code. The target at this stage is to make the code cleaner, understandable, and manageable without altering its behavior. The principle revolves around two major activities:
- a. Remove duplication: The mantra, “three strikes and you refactor,” is all about preventing code repetition.
- b. Improve names of variables, classes, methods, modules, and packages and formatting the code for readability.
Refactoring helps to:
- a. Promote code reuse.
- b. Improve the design of software.
- c. Facilitate easier future modifications.
For instance, considering the previous example, if more test cases were added to validate the inputs and these tests passed with duplicated code, the code needs to be refactored to remove such duplications.
Conclusion
In conclusion, TDD’s Red-Green-Refactor cycle allows developers to focus on smaller, manageable pieces of functionality one at a time, resulting in a robust and easily maintainable codebase. It increases confidence in the code and makes it less prone to bugs, which can significantly reduce the debugging time. Adhere to these guiding principles, and you are on your way to acing the Advanced Certified Scrum Developer (A-CSD) exam.
Practice Test
True or False: Test Driven Development (TDD) prioritizes writing failing tests before starting the software development phase.
- True
- False
Answer: True
Explanation: The initial step in TDD is to write a failing test. It allows the developer to understand what needs to be designed.
Which of the following are the guiding principles of TDD?
- A. You can only write code to make a failing test work.
- B. Write the minimum amount of code required to pass a test.
- C. Re-factoring code is unnecessary and time-consuming.
- D. Repeatedly run the test until the newly implemented code passes.
Answer: A, B, D
Explanation: C is false. After code passes a test, refactoring is done to ensure code readability, maintainability, and optimization.
True or False: TDD dictates that the same person who wrote the tests should refactor the code.
- True
- False
Answer: False
Explanation: TDD does not enforce that the same person should write the tests and refactor the code.
Why is refactoring considered a necessary part of TDD?
- A. It helps maintain code readability.
- B. It ensures code optimization.
- C. It streamlines the execution of complex test cases.
- D. All of the above.
Answer: D
Explanation: Refactoring helps to improve the design of existing code, thereby making it more readable, easily maintainable, and optimized.
True or False: TDD follows a “test first” development approach.
- True
- False
Answer: True
Explanation: TDD follows a “test first” approach where tests are written first before writing the code.
In the TDD environment, a test ____
- A. Remains useless until the code is written
- B. Is written only after the code is developed
- C. Guides the development of the target functionality
- D. Is a secondary requirement
Answer: C
Explanation: To drive the functionality, the test is written first in TDD.
True or False: TDD is about developing software in shorter, more manageable iterations.
- True
- False
Answer: True
Explanation: TDD is about developing software in shorter, iterative cycles, where each cycle includes writing a test, making it run, and refactoring.
Which of the following does not describe TDD?
- A. Write tests before code
- B. Don’t write a line of new code unless it is for passing a failing test
- C. Spend most of your time creating complex test cases
- D. Constant refactoring to increase readability
Answer: C
Explanation: TDD is not about spending most of your time creating complex test cases, but about ensuring the code works as expected through simple tests.
True or False: In TDD, tests are written based on the code.
- True
- False
Answer: False
Explanation: In TDD, tests are written first, followed by the code.
The aim of TDD is to:
- A. Create more bugs.
- B. Develop code with fewer bugs.
- C. Build complex software designs.
- D. Create documentation.
Answer: B
Explanation: The aim of TDD is to develop a bug-free code; it makes the code easier to understand and refactor.
Interview Questions
Can you state the first guiding principle of Test-Driven Development (TDD)?
The first principle is that you must write a failing test before you write any production code.
Why is it necessary to write a failing test in TDD?
Writing a failing test ensures that the test is valid and not giving false positives. It also sets a clear goal for what the production code must accomplish.
What is the second principle of TDD?
The second principle is that you should only write enough production code to make the failing test pass.
Why should you only write production code to make the test pass in TDD?
Writing just enough code to pass the failing test minimizes the chance of introducing unnecessary complexity or bugs. It helps in focusing on one requirement at a time.
What is the necessity of refactoring code in TDD?
Refactoring is necessary to keep the code simple and clean. This minimization of complexity leads to code that’s easier to maintain and debug.
Can you mention the third principle of TDD?
The third principle is refactoring. After the test passes, you should refactor the code to remove any duplication or unnecessary complexity.
How does TDD help in reducing bug introduction in the code?
As TDD emphasizes on writing tests first and enough production code just to make that test pass, it helps in focusing on requirements and functionalities one at a time. This approach minimizes the chances of introducing bugs.
How does the principle of writing a failing test serve in TDD?
Writing a failing test first helps to illustrate the problem that the code needs to solve. It provides a goal for the code and ensures that the test is not passing erroneously.
What is the purpose of writing just enough code to pass the test in TDD?
The purpose is to ensure that the functionality is adequately met without introducing unnecessary complexity or bugs, keeping things as simple and efficient as possible.
How does refactoring play a role in the principles of TDD?
Refactoring is done to improve the design of the already working code. It makes the code more readable, understandable, and maintainable without changing its behavior. It’s the principle that ensures the cleanliness of the code after each test pass.
Can you explain why these principles of TDD are necessary?
These principles structure the development process such that code is written to meet requirements as directly as possible. This leads to cleaner, more efficient, and more maintainable code. It averts potential digressions and minimises the chance of introducing bugs. It also encourages thinking about the design before diving into implementation.
How can the principles of TDD lead to better code design?
By focusing on one small piece of functionality at a time, TDD encourages modular and decoupled design. The process of refactoring also encourages programmers to continually re-evaluate and improve their design.
How does following the principles of TDD aid in the process of debugging?
Since each piece of production code is written to make a specific test pass, when a test fails, it’s easier to identify the problem area. This makes debugging a much easier process.
What role do these TDD principles play in code maintainability?
The simplicity and clarity inherent in TDD often result in highly maintainable code. Persistent refactoring results in code that is free from duplication and unnecessary complexity, making it easier to adapt to changing requirements.
Can you explain the importance of the principle of writing a failing test first in TDD?
Writing a failing test first ensures that the implementation code is testable. It also guarantees that the test itself is necessary and correct, as it will fail if the expected functionality does not exist or if the test is incorrect.
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