Testing Strategies: Iterative and Final Testing

This lesson covers testing strategies as required by OCR J277 Section 2.4. Testing is the process of checking that a program works correctly and meets its requirements. OCR requires you to understand both iterative testing (testing during development) and final/terminal testing (testing the completed program).

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Why Is Testing Important?

Testing is essential because:

• It identifies bugs (errors) before the program is used by real users.
• It verifies that the program meets its requirements — does it do what it is supposed to do?
• It ensures the program handles unexpected inputs and edge cases gracefully.
• It builds confidence that the program is reliable and robust.

A program that has not been thoroughly tested may contain hidden bugs that cause crashes, security vulnerabilities, or incorrect results.

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Iterative Testing

Iterative testing is testing that takes place during development, after each new section of code is written. The programmer tests individual modules or features as they build them, fixing errors before moving on.

How Iterative Testing Works

1. Write a small section of code (e.g. a function or feature).
2. Test it with various inputs to check it works correctly.
3. Fix any errors found.
4. Re-test to confirm the fix works and has not introduced new errors.
5. Move on to the next section of code.
6. Repeat the cycle throughout development.

Benefits of Iterative Testing

Benefit	Explanation
Early bug detection	Errors are found close to when they were introduced, making them easier to fix
Easier debugging	Only a small amount of new code needs to be checked
Continuous improvement	Code quality improves throughout development
Reduced risk	Problems are caught incrementally rather than all at the end

Example of Iterative Testing

A programmer building a quiz application might test:

1. First, test that questions display correctly.
2. Then, test that user answers are recorded.
3. Then, test that the score is calculated correctly.
4. Then, test that the results are saved to a file.

Each feature is tested individually before the next one is built.

flowchart LR
    A[Write small section of code] --> B[Test with normal/boundary/erroneous data]
    B --> C{Bugs found?}
    C -- Yes --> D[Fix code]
    D --> E[Re-test the same data]
    E --> C
    C -- No --> F[Move to next feature]
    F --> A
    F -.->|All features done| G[Final / Terminal testing]
    G --> H{Integration OK?}
    H -- No --> D
    H -- Yes --> I[Release-ready robust program]

OCR Exam Tip: When describing iterative testing, always emphasise that testing happens DURING development, not just at the end. The key word is "iterative" — meaning repeated cycles of code, test, fix, re-test.

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Final (Terminal) Testing

Final testing (also called terminal testing) takes place when the program is complete. The entire program is tested as a whole to ensure all components work together correctly and the program meets all its requirements.

How Final Testing Works

1. The complete program is tested against the original requirements.
2. All features are tested together to check they integrate correctly.
3. A comprehensive set of test data is used (normal, boundary, erroneous).
4. The program is checked for usability — is it easy to use?
5. Performance is checked — does it run efficiently?
6. Security is checked — can it be exploited?

Benefits of Final Testing

Benefit	Explanation
Complete coverage	Tests the entire program as a whole
Integration testing	Checks that all modules work together
Requirements verification	Confirms the program meets its specification
User acceptance	Ensures the program is suitable for end users

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Iterative vs Final Testing

Feature	Iterative Testing	Final Testing
When	During development	After development is complete
What is tested	Individual modules/features	The complete program
Purpose	Find and fix bugs early	Verify the program meets all requirements
Scope	Small sections of code	Entire system
Frequency	Continuous — after each change	Once (or repeated if bugs are found)

Which Is Better?

Neither is "better" — they complement each other:

• Iterative testing catches bugs early when they are cheap and easy to fix.
• Final testing ensures the complete program works as a whole.
• Both should be used for a robust development process.

OCR Exam Tip: If asked "explain the difference between iterative and final testing" (a common 4-mark question), structure your answer as: iterative testing happens during development on individual modules, while final testing happens after completion on the whole program. Give an example of each.

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Test Plans

A test plan is a document that describes what will be tested, what test data will be used, and what the expected outcomes are.

Test Number	Description	Input	Expected Output	Actual Output	Pass/Fail
1	Valid age	25	"Welcome"
2	Boundary age	18	"Welcome"
3	Below range	-1	"Invalid age"
4	Non-numeric	"abc"	"Please enter a number"

The "Actual Output" and "Pass/Fail" columns are filled in during testing.

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Types of Testing (Extended Knowledge)

Type	Description
Unit testing	Testing individual subroutines or modules
Integration testing	Testing that modules work together
System testing	Testing the complete system
User acceptance testing	End users test to confirm it meets their needs
Alpha testing	Testing by the developer's team
Beta testing	Testing by a group of external users

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Summary

• Iterative testing happens during development, testing individual features as they are built.
• Final testing happens after development, testing the complete program.
• Both approaches should be used together for thorough testing.
• A test plan documents what will be tested, with expected and actual outcomes.
• Testing helps identify bugs, verify requirements, and ensure robustness.