Test Data & Plans
Testing "10" and "20" isn't enough. You must actively try to break your own algorithm by throwing Boundary and Invalid/Erroneous data at it.
The Three Data Types
Imagine an algorithm that asks for a student's test score, which must be between 1 and 100.
Normal
Standard, expected data.
50, 75, 80
Boundary
The absolute extreme valid edges.
1, 100
Invalid / Erroneous
Rule-breaking OR wrong type.
200, 0, "Ten"
Examiner's Eye - The Myth of Invalid vs Erroneous
Historically, "Erroneous" meant wrong data type and "Invalid" meant out of bounds. The official OCR guidance explicitly flags this as a widespread myth. Both terms are now completely synonymous. ANY test data that breaks the rules is considered both Invalid and Erroneous. (Also, you no longer need to know the phrase "invalid boundary"!).
Example Test Plan (Rule: Score 0-100)
| Test Number | Data Category | Data Used | Expected Outcome |
|---|---|---|---|
| 1 | Normal | 50 | Data accepted. |
| 2 | Boundary | 0 and 100 | 0 accepted. 100 accepted. |
| 3 | Invalid/Erroneous | 101 or "Hello" | Type/Range error. Loop triggers. |
The Validation Sandbox
Validation Rule: 1 <= Age <= 100.
Type absolutely anything into the box below. The engine will instantly classify your test data.
Check Your Understanding
1. An algorithm asks for a User Rating between 1 and 5 (Integer). A tester inputs '99'. What category of test data is this?
2. The rule is "Password must be exactly 8 characters long". Which of the following is an example of Boundary Data?
Written Exam Scenario (AO2/AO3)
Stretch (Grade 9)"A login programme requires a string username. The validation rule states the username must be between 3 and 10 characters long, inclusive. Draw a brief test plan table providing exactly one piece of Normal, Boundary, and Invalid test data that could be used." (3 marks)
| Category | Data Provided |
|---|---|
| Normal | "Admin" (5 chars) |
| Boundary | "Bob" (3 chars) or "SuperAdmin" (10 chars) |
| Invalid / Erroneous | "A" (1 char, fails rule) OR 15 (Wrong type) |