Stretch tasks Producing Robust Programs

Round 1: Quiz Blitz

1. Range check A range check tests that a value falls between an upper and a lower limit.
2. Presence check A presence check makes sure something has been entered.
3. False Validation checks data is sensible. Verification checks it was entered correctly.
4. Runtime error The code is valid, but it crashes while running.
5. Syntax error It breaks the rules of the language, so the program cannot run.
6. Logic error It runs perfectly and quietly gives the wrong answer: a logic error.
7. 11; 18 Boundary data sits at the very edge of the range. 14 is normal, 25 is invalid, and text is erroneous.
8. iterative testing Iterative testing finds problems early, when they are cheap to fix.
9. Confirms a user is who they claim to be Passwords, two factor authentication and biometrics are all ways to authenticate.
10. Meaningful variable names; Comments explaining why Indentation, subroutines and constants help too.
11. A stolen database does not reveal them A hash cannot simply be read back as the password.
12. True Without an expected result, there is nothing to compare the actual result with.

Round 2: Quick Fire

1. • Validation checks that data is sensible and in the right format
   • Verification checks that data was entered correctly, for example by typing it twice
   Model answer

   Validation checks that data is sensible and in the right format before it is used. Verification checks that it was entered correctly, for example by asking for a password twice.

2. • Normal: a typical age inside the range
   • Boundary: a value at the edge of the range
   • Erroneous: data of the wrong type
   Model answer

   Normal: 14. Boundary: 11. Erroneous: "fourteen", which is text rather than a number.

3. • Meaningful identifiers
   • Comments
   • Indentation
   • Subroutines
   • Constants
   • White space
   Model answer

   Use meaningful variable names, such as totalPrice instead of tp, and add comments that explain why the code does something.

4. • It tests the very edge of the allowed range
   • That is where off by one mistakes, such as > instead of >=, are caught
   Model answer

   Boundary data tests the very edge of the allowed range, which is exactly where off by one mistakes hide: a check written as > 11 instead of >= 11 is only caught by testing 11.

Round 3: Big Think

1. • A presence check on the username
   • A length check on the username
   • A type check that the age is a whole number
   • A range check on the age
   • A loop asks again until the input is valid, instead of crashing
   • An error message tells the user what to enter
   • This is defensive design: it anticipates misuse
   Model answer

   A presence check makes sure the username is not left blank, and a length check could make sure it is at least 3 characters long. A type check makes sure the age is a whole number, so typing letters cannot crash the program, and a range check makes sure it is between 13 and 100. If any check fails, the program shows an error message that tells the user what to enter, and a while loop asks again until the input is valid. This is defensive design: it anticipates misuse instead of crashing.

2. • Iterative testing happens during development, as each part is written
   • So problems are found early, when they are cheap to fix
   • Final testing happens when the program is complete
   • It checks the program against the original requirements
   • Parts that work alone can still fail when combined
   Model answer

   Iterative testing happens during development: each part is tested as it is written and corrected before moving on, so problems are found early, when they are cheap to fix. Final testing happens when the program is complete: the whole program is tested against the original requirements. Each part can work on its own while the parts fail when combined, so testing the whole program together is still needed.

This or That

1. An email must contain an at sign A format check tests for a pattern. Not blank is a presence check.
2. Verification Typing it twice checks it was entered correctly: verification.
3. A logic error The translator finds syntax errors for you. A logic error runs quietly with the wrong answer.
4. 11 Only a test on the boundary itself shows the difference.
5. Erroneous Erroneous data is the wrong type entirely, and should be rejected.
6. A second check, such as a code sent to a phone A stolen password alone is no longer enough to get in.
7. A runtime error The code is valid, so it starts, then crashes while running.
8. The original requirements It confirms the program does everything it was supposed to.

Memory Match

• A 5 Range check: Between a lower and an upper limit
• B 4 Presence check: Something has been entered
• C 6 Length check: The right number of characters
• D 3 Syntax error: Breaks the language's rules, so it won't run
• E 1 Logic error: Runs, but gives the wrong result
• F 2 Boundary data: Values at the very edge of the range

Sort It

1. Runtime error Dividing by zero The program crashes while running.
2. Runtime error Reading item 10 of a list with 5 items The index is out of range, so the program crashes.
3. Logic error Using > where >= was needed The program runs, but gets the boundary wrong.
4. Logic error Printing the average before it is calculated The steps are in the wrong order, so the output is wrong.
5. Logic error Using + where * was intended It runs, but the answer is wrong.
6. Syntax error A bracket that is never closed Unclosed brackets break the language's rules.
7. Syntax error A missing colon after an if statement It breaks the rules of Python, so it will not run.
8. Logic error A loop that adds 1 to the wrong variable No crash, just a wrong result.
9. Runtime error Converting the text abc to a whole number int() fails on letters while the program runs.
10. Runtime error Opening a file that does not exist The code is fine, but it fails at run time.
11. Syntax error A misspelled keyword, such as whlie The translator cannot understand the misspelled keyword.