ATA: ISTQB Advanced Level Test Analyst

Under the classification tree method, the minimum number of test cases needed for basic (each-class-at-least-once) coverage equals the largest number of classes that must be exercised across any classification, since each test case can select only one class per classification. Pairing Colour's three classes with the three distinct Shape/Size leaf combinations (Circle; Triangle-Small; Triangle-Large) into three test cases covers every classification value exactly once, making three the minimum required.