CTFL 4.2.3: Use decision table testing to derive test cases
K3Syllabus section 4.2.3
4 original PrepBench practice questions for learning objective 4.2.3 of the CTFL 4.0 syllabus. Try the examples below and check each answer against its syllabus reference.
Practice questions
Question 1
A loan application system evaluates three conditions: Condition 1: the applicant is an existing customer. Condition 2: the applicant's credit score is above 700. Condition 3: the applicant requests more than 50,000. Any combination in which the applicant is not an existing customer and requests more than 50,000 is infeasible, because only existing customers may request that amount. The full decision table covers every combination of the three conditions. After the infeasible columns are deleted, how many columns remain to be exercised?
- 4
- 5
- 6
- 8
Show answer
- 4This would delete four columns; only the two with Condition 1 false and Condition 3 true are infeasible.
- 5This deletes three columns, but Condition 2 is free in only two of them.
- Correct answer: 68 full columns minus the 2 infeasible ones leaves 6 feasible columns.
- 88 is the size of the full table before the infeasible columns are deleted.
A full decision table has enough columns to cover every combination of conditions, so three Boolean conditions give 2 x 2 x 2 = 8 columns. The infeasible combination fixes Condition 1 as false and Condition 3 as true, while Condition 2 remains free, which describes 2 of those columns. Deleting them leaves 6 feasible columns, and in decision table testing the coverage items are exactly the columns containing feasible combinations.
Syllabus section 4.2.3
Question 2
A shipping system uses the decision table below. Condition 1 is that the customer is a member; Condition 2 is that the order value exceeds 100. Rule 1 — Condition 1: true; Condition 2: true; actions: free shipping and a gift. Rule 2 — Condition 1: true; Condition 2: false; actions: the gift. Rule 3 — Condition 1: false; Condition 2: true; actions: free shipping. Rule 4 — Condition 1: false; Condition 2: false; actions: none. A customer who is not a member places an order with a value of 250. Which rule applies, and what does the customer receive?
- Rule 1 — free shipping and a gift
- Rule 2 — the gift only
- Rule 4 — nothing
- Rule 3 — free shipping only
Show answer
- Rule 1 — free shipping and a giftRule 1 requires Condition 1 to be true, but this customer is not a member.
- Rule 2 — the gift onlyRule 2 requires Condition 1 true and Condition 2 false; neither holds here.
- Rule 4 — nothingRule 4 requires Condition 2 to be false, but 250 does exceed 100.
- Correct answer: Rule 3 — free shipping onlyCondition 1 false and Condition 2 true is Rule 3, which gives free shipping.
Each column of a decision table corresponds to a decision rule defining a unique combination of conditions together with the associated actions. Here Condition 1 is false, because the customer is not a member, and Condition 2 is true, because 250 exceeds 100. That combination is Rule 3, whose only action is free shipping.
Syllabus section 4.2.3
Question 3
A ticket system's rules are recorded as a decision table with two conditions: Condition 1: the customer holds a loyalty card Condition 2: the booking is made more than 14 days in advance Rule 1: C1 true, C2 true -> 10% discount and free seat selection Rule 2: C1 true, C2 false -> free seat selection only Rule 3: C1 false, C2 true -> 10% discount only Rule 4: C1 false, C2 false -> 5 EUR handling fee Three tests have run: a card holder booking 30 days ahead, a card holder booking 3 days ahead, and a customer without a card booking 3 days ahead. Which further test is needed for 100% decision table coverage, and what must it produce?
- A booking without a card made 30 days ahead, producing a 10% discount only
- A booking with a card made 30 days ahead, producing a discount and free seat selection
- A booking without a card made 3 days ahead, producing a 5 EUR handling fee
- A booking without a card made 30 days ahead, producing a 5 EUR handling fee
Show answer
- Correct answer: A booking without a card made 30 days ahead, producing a 10% discount onlyThis is the only uncovered column, rule 3, and its single action is the 10% discount.
- A booking with a card made 30 days ahead, producing a discount and free seat selectionThese inputs match rule 1, which the first executed test already covers.
- A booking without a card made 3 days ahead, producing a 5 EUR handling feeThese inputs match rule 4, which the third executed test already covers.
- A booking without a card made 30 days ahead, producing a 5 EUR handling feeThe inputs identify rule 3 correctly, but rule 3 grants the discount rather than the handling fee.
In decision table testing the coverage items are the columns containing feasible combinations of conditions, and 100% coverage requires test cases to exercise all of them. The three executed tests exercise rule 1 (card, 30 days), rule 2 (card, 3 days) and rule 4 (no card, 3 days). Rule 3 — no card, more than 14 days ahead — is the only column left, and its action is the 10% discount alone.
Syllabus section 4.2.3
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