Tax rates on income are: 0% for up to 5000 EUR, 10% is added for each additional 5000 EUR up to 20,000 EUR, and 40% is applied for above 20,000 EUR…

Equivalence Partitioning is a black-box test design technique where test cases are designed to exercise representative values from partitions. The tax rules create five distinct valid partitions for income:

1. Up to 5,000 EUR

2. 5,001 to 10,000 EUR

3. 10,001 to 15,000 EUR

4. 15,001 to 20,000 EUR

5. Above 20,000 EUR

The principle is to select one test value from within each partition. Option B (3000, 6000, 12000, 19000, 30000) is the only choice that provides a single, representative value from each of these five valid partitions, thus achieving 100% coverage for this technique.

A: Includes -1000, which belongs to an invalid equivalence partition (negative income), whereas the question specifically asks for valid partitions.

C: This set is incomplete as it fails to select any test values for the partitions covering incomes from 5,001-10,000 and 10,001-15,000 EUR.

D: This set is incomplete as it fails to select a test value for the partition covering incomes from 10,001-15,000 EUR.

1. ISTQB® Certified Tester Foundation Level Syllabus (CTFL) 2018 V3.1.1. Section 4.2.1, "Equivalence Partitioning," states: "Test cases are designed to cover each partition at least once... Coverage is measured as the number of equivalence partitions tested... divided by the total number of identified equivalence partitions." This principle directly supports selecting option B, which covers all five identified partitions.

2. Jorgensen, P. C. (2013). Software Testing: A Craftsman's Approach, Fourth Edition. CRC Press. In Chapter 7, "Domain Testing," the methodology for equivalence class testing is detailed. It specifies identifying partitions (classes) and selecting one representative value from each class as the minimum requirement for test cases, which validates the approach of choosing one value per identified tax bracket.

3. MIT OpenCourseWare. (2010). 6.170 Software Studio, Lecture 2: Testing. Massachusetts Institute of Technology. The lecture notes on black-box testing explain the strategy of partitioning the input space into equivalence classes where the program is expected to behave similarly. The testing strategy is to "pick one input from each class," which is precisely what option B accomplishes for the given problem. (Available at: ocw.mit.edu)