Programming Basics: Test the Edges

Turn a requirement into test cases before editing a program.

All worksheets

5 questions0m 0s

Learn the skill

Requirement: accept whole-number levels from 1 through 5, inclusive. Valid types are integers only. Build tests for each endpoint, just outside each endpoint, an ordinary interior value and a wrong type. A passing sample is evidence, not a universal proof.

Worked example

For integer inputs 0, 1, 3, 5 and 6, expected outcomes are reject, accept, accept, accept and reject. The text "3" is rejected under this contract even though it contains a digit.

The contract accepts only integers from one through five. Integer zero is rejected, one and five are accepted, and six is rejected. The text string three is rejected because it is not an integer.

Would you believe it?

A digit can be stored as text rather than as a number. The string "3" and the number 3 can look alike on a screen while needing different treatment in a program.

Python documentation: numbers and strings

Question 1 Should integer 1 be accepted? No Only after conversion Yes

Question 2 Should integer 6 be accepted? Only on a second attempt No Yes

Question 3 Should the text "3" be accepted under this contract? No Yes Text and numbers are always identical

Question 4 A bug uses level < 5 instead of level <= 5. Which test exposes it? Integer 3 Integer 0 Integer 5

Question 5 Do these few passing examples prove correctness for every possible input? Only if run twice No Yes

Review your work

0correct

Complete the questions to review each answer.

View dashboard