Errors, testing and debugging

Lesson overview

Use test data, expected results and debugging steps to find and fix programming errors.

Focus: Errors, testing and debugging.

What you will learn

• Distinguish syntax, logic and runtime errors.
• Choose normal, boundary and invalid test data.
• Use expected results to judge whether a test passed.
• Describe debugging as finding, isolating and fixing errors.

Before you start

• Variables, conditions and loops.
• Validation checks.
• Trace tables and dry runs.

Test-plan examples

Use the mark-grade and password examples below to build a small test table with input, expected result and actual result.

Errors, testing and debugging infographic

Explanation

Testing is planned checking. A good test table states the input, the expected result, the actual result and whether the test passed.

Normal test data should be accepted, boundary data checks edges of valid ranges, and invalid data should be rejected or handled safely.

A syntax error breaks the language rules, a logic error runs but gives the wrong result, and a runtime error happens while the program is running.

Worked examples

Quick checks

Practice

Exam practice ladder

• Fluency: recall the key term and use it accurately.
• Application: apply the idea to the scenario rather than giving a generic definition.
• Algorithmic reasoning: show the steps, condition or variable change clearly.
• Evaluation: explain why one method, structure or control is suitable.

Answers and marking guidance

Exact answers and marking guidance are hidden under each question. For this lesson, earn marks by naming the correct Computer Science idea, applying it to the scenario and showing the logic or value change clearly.

Common mistakes

• Only testing one normal value.
• Forgetting invalid data when validation is part of the program.
• Writing actual results before running the test.
• Calling every mistake a syntax error.

Extension

Create a test table for a function that returns true only when a username is 4 to 12 characters long.

Next lesson

Next, continue with Binary and Denary Conversion.

Exam-board guidance

Aplailasain is an independent learning resource and is not endorsed by any exam board.