Testing a spreadsheet

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8.2 · Chapter 8 · AS Level IT · Hodder Education

Testing a Spreadsheet

How to design a test plan, choose the right test data, test formulas and validation rules, and what to do when you find errors.

📋 Test Plans

🟢 Normal Data

🟡 Extreme Data

🔴 Abnormal Data

The Big Idea: Testing is not an afterthought — you design your test plan before entering any data. A good test plan systematically checks every formula and every validation rule using carefully chosen data that covers normal use, edge cases, and deliberate errors.

WhyWhy Testing Matters

A spreadsheet that looks right may still contain errors in formulas or validation rules that only appear under specific conditions. Thorough testing before using real data reduces errors, builds confidence in the model, and protects the integrity of any decisions made using the spreadsheet.

All formulas and all validation rules need to be tested. For formulas containing conditions (IF, COUNTIF, INDEX, MATCH, etc.) — every branch of the condition must be tested.

Data TypesThe Three Types of Test Data

🟢 Normal Data

Data that is valid and within the expected range. The formula or validation rule should accept it and produce the correct result.

Example (scores 0–10): Test with 1, 4, 8 — all should be accepted.

🟡 Extreme Data

Data that is on the boundary of what is valid — the exact minimum or maximum allowed value. These are still valid and should be accepted, but they test whether the boundary condition is coded correctly.

Example (scores 0–10): Test with exactly 0 and exactly 10.

🔴 Abnormal / Erroneous Data

Data that is outside the valid range or of the wrong type. The validation rule should reject it with an error message.

Example (scores 0–10): Test with −14, 1004, 1.3, 5.6 — all should be rejected.

⚠️ Extreme data is the most important to test. It catches errors like using > instead of >= (greater than vs greater than or equal to). A boundary that should be accepted but isn't (or vice versa) is a common mistake that only extreme data will catch.

Note on text/list validation

List-based validation (e.g. only "AMD" or "Intel") has no extreme data — text values in a list cannot have boundaries. Only normal (valid list items) and abnormal (mis-spelled or invalid items) data types apply.

StructureHow to Design a Test Plan

A test plan is created before any data is entered into the spreadsheet. It should specify exactly what data will be used, what result is expected, and (after testing) what the actual result was. If the actual result doesn't match, remedial action must be taken.

A test plan table has these columns:

Test type	What is being tested	Data entered	Expected result
Normal	Cell C8 (scores 0-10)	4	Data accepted
Normal	Cell C8	8	Data accepted
Extreme	Cell C8 (minimum)	0	Data accepted
Extreme	Cell C8 (maximum)	10	Data accepted
Abnormal	Cell C8	-14	Validation error message
Abnormal	Cell C8	1.3	Validation error message
Abnormal	Cell C8	1004	Validation error message

Green border = normal · Amber border = extreme · Red border = abnormal. The Actual result and Remedial action columns are completed after testing.

FormulasTesting Formulas

calculate the expected result by hand before entering the formula

Choose simple test values

Calculate expected result by hand

before

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📋 Summary & Review
✅ Concepts Checklist
🧠 What to Memorise
🎯 Exam Tips

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Testing a spreadsheet