Specification by example
Specifying a business rule with concrete examples: key examples, example tables, boundary values, an example that reveals a missing rule and Gherkin scenarios the client can read.
- 24 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- The numbers
A few cards from the deck
Business rule: what is it?
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A general statement of how the organisation decides or calculates, independent of any screen: “free delivery from €50”.
A general sentence lets ambiguities through (does “from €50” include €50?). Worked examples are there to remove them.
The rule says “free delivery from €50”. Which example reveals whether the threshold is included?
- A basket of €50.00
- A basket of €49.99
- A basket of €50.01
- A basket of €100.00
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A basket of €50.00
Only the exact value of the threshold says whether the rule means “greater than or equal to” or “strictly greater than”. At €49.99 the fee is due in both readings; at €50.01 and €100 delivery is free in both.
In a Gherkin scenario outline, the variable values are written in …, like <amount>, and filled from a table introduced by ….
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In a Gherkin scenario outline, the variable values are written in angle brackets, like <amount>, and filled from a table introduced by Examples.
Each row of the table runs the scenario once, replacing each parameter with the value in its column.
Key example: what is it?
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A concrete, numerical case, shared with the client, that illustrates a rule and is kept because it covers something the others do not.
Two examples of the same kind (€60 and €70 for “free from €50”) say nothing more than one of them: only one is kept.
The rule says “free from €50”. The client gives the example “€60 to Corsica: €8 delivery fee”. What does the example reveal?
- A typing error to remove from the table
- An exception the written rule leaves out
- A case too rare to be specified
- A flaw in the team's scenario outline
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An exception the written rule leaves out
When an example contradicts the written rule, the rule is often incomplete: here a geographic exception nobody had stated. The example has done its job.