iⁿ spreadsheet testing methodology — Conclusion

Over many years of working with spreadsheets, we have developed the iⁿ methodology for testing that a spreadsheet does what it is supposed to do. The iⁿ methodology involves asking five key questions regarding each of five aspects of the spreadsheet.

That is:

• Intent. Is the spreadsheet fit-for-purpose? Is the spreadsheet solving the right problem? Do stakeholders understand the intent of the spreadsheet? Does the spreadsheet answer all necessary questions? Is the scope limited to only the required tasks?
• Instructions. Are there clear instructions about how to use the spreadsheet? Does the spreadsheet include instructions for developers? Are all the instructions up-to-date? Are all data sources defined? Does all the data have units specified?
• Instruments. Are the instruments (techniques, tools, and algorithms) appropriate? Would other instruments be better? Do stakeholders understand the spreadsheet's instruments? Do the developers understand the instruments? Are limitations and caveats clearly stated?
• Implementation. Are the instruments implemented correctly? Is the design intuitive, easy to use, and robust? Is there separation between data and calculations? Does the spreadsheet have access and version control? Is recalculation time an issue?
• Immunity. To what extent is the spreadsheet immune to errors? How well does the spreadsheet handle invalid data? Is the spreadsheet easy to modify without creating errors? Are the error messages adequate? Does the spreadsheet fail gracefully when necessary?

The iⁿ spreadsheet testing methodology is summarised in the diagram below.

Summary of the iⁿ spreadsheet testing methodology

The iⁿ methodology is a comprehensive approach to spreadsheet testing, consisting of five parts: Intent, Instructions, Instruments, Implementation, and Immunity — each of which asks five key questions.

Stakeholders can have confidence in the spreadsheet only when all the iⁿ spreadsheet testing methodology questions have been answered satisfactorily. An inadequate answer to any of these questions indicates that decisions that depend on that spreadsheet may be wrong, and hence the spreadsheet poses a risk to your organisation.

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