Lesson 5: C++ toolchain and basics: Testing focus

Concept Explanation

Testing focus means checking behavior on purpose instead of assuming that a program is correct because it compiled once. In this lesson, you will use a small C++ example to see how a direct assertion can protect a basic function from silent mistakes. The point is not to build a large test suite yet. It is to practice thinking in expected results: given this input, what should happen, and how can I verify it immediately?

Where to Put the Code

1. Start with variables and inputs. Keep includes, main function, and data types explicit.
2. Add processing logic in the middle section.
3. Finish with output and quick validation.

Command Reference

• State the expected output for each test case before you run the program.
• Add one more assertion that checks a different but valid input pattern.
• Keep the tested function simple so the purpose of each check is easy to understand.
• Use the program output to confirm when all assertions have passed.

Step-by-step Guide

1. Run the example once and confirm that both checks complete without failing.
2. Read each assertion and explain what behavior it is protecting.
3. Add one more test case for a small edge condition such as adding zero.
4. Break one assertion on purpose, run the code, and observe how the failure is reported.
5. Restore the correct expectation and verify the program passes again.

Practice Exercises

• Write a similar test for a subtract function with two different inputs.
• Add a test case that checks repeated values such as add(4, 4).
• Create a tiny report message that prints only after all checks succeed.

Coding Challenges

• Design three small tests that would quickly catch a bug in a basic arithmetic helper.
• Compare testing with assert against testing only by printing values, and explain which gives faster feedback here.

Mini Practice Tasks

• Rename one parameter so the function reads more clearly.
• Add one successful assertion and rerun the program.
• Write one sentence describing what the tests guarantee.