Oedipus and the testing Sphinx
A long time ago, in ancient Greek, Oedipus was travelling to Thebe. On his way, he crossed the path of a Sphinx. The Sphinx stopped all travellers on the road to Thebe to ask them a riddle. If they were not able to answer the riddle correctly, they would be killed and eaten. If the travellers were able to answer the riddle correctly, they could continue their journey. The Sphinx asked Oedipus this riddle: ‘What walks on four feet in the morning, two in the afternoon and three at night?’ Oedipus took a short moment to think and answered: ‘Man: as an infant, he crawls on all fours; as an adult, he walks on two legs and in old age, he uses a ‘walking’ stick’. The Sphinx, puzzled by the fact that somebody actually was able to answer the question, allowed Oedipus to continue his journey to Thebe.
Now the testing Sphinx asks you: ‘What walks on four feet in the morning, two in the afternoon and three at night?’ You give him the same answer as Oedipus did. But she is not puzzled by the fact you are able to answer the question. Instead, she challenges you to give the smallest amount of test cases to test the theorem. If you are able to give the Sphinx the correct test cases, she will let you continue your journey. If not … you have to do overtime forever.
As a seasoned tester, you know what to do: use boundary analysis to identify the test cases. So first you check what the age groups are. The answer is 0-17, 18-64 and 65 and up. You define the minimum required test cases as 17, 18, 64 and 65. You choose these test cases, because you know that to test the boundaries, you will need to test the smallest possible step from the boundary, in this case 1 (year).
The Sphinx is puzzled by your testing knowledge and accepts your answer. You are allowed to continue your work without having to do overtime. But beware! The Sphinx may come back with another riddle, even more difficult. If you cannot answer the riddle … it is overtime forever for you.