GCSE Computer Science Revision — Testing, Robustness & Defensive Design
Revise Testing, Robustness & Defensive Design for GCSE Computer Science with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is Testing, Robustness & Defensive Design?
Robustness and defensive design are about creating programs that can handle unexpected inputs and situations without crashing. This involves anticipating potential problems, such as users entering the wrong data type, and adding code to handle these errors gracefully. Testing is the process of finding errors in a program, using different types of test data (normal, boundary, and erroneous) to ensure the code works as expected.
Board notes: All boards (AQA, Edexcel, OCR) place a strong emphasis on testing and creating robust programs. You will be expected to devise test plans and write code that includes validation and error handling.
Step-by-step explanationWorked examples
Worked example
A program asks for a user's age. A defensive design would not assume the user enters a number. In Python, you could use a `try-except` block. `try:` to convert the input to an integer. If it fails (e.g., the user typed 'abc'), the `except` block would catch the `ValueError` and print a message like 'Invalid input. Please enter a number.' instead of crashing.
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Common mistakes
- 1Only testing with normal data that you expect the program to work with. You must also test the boundaries (e.g., the highest and lowest valid numbers) and with erroneous data (e.g., text when a number is expected).
- 2Confusing robustness with correctness. A correct program does what it's supposed to do. A robust program keeps working even when things go wrong.
- 3Not providing helpful error messages. A good defensive design tells the user what they did wrong and how to correct it, rather than just crashing.
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Frequently asked questions
What are the different types of testing?
Iterative testing is testing done as you build the program. Final/terminal testing is done on the completed program. Normal test data is valid data you expect to work. Boundary data tests the limits of what is acceptable. Erroneous data is invalid data that the program should reject.
What is input validation?
Input validation is the process of checking if data entered by a user is valid. This could involve checking the data type, the length of a string, or if a number is within a certain range.