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Grade 9 · unit review

Review: Build Evidence for Small Functions

Test a function’s contract, boundaries and list structure, then retain regression cases.

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Bring the unit skills together

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Unit review questions
1. A fictional classifier returns junior for integer level < 5, standard otherwise. Which test detects replacing < 5 with ≤ 5?
2. Contract: integer x in 0..6, Boolean values excluded; low if x < 2, high otherwise. What is expected for 7?
3. A faulty sum visits positions 0 up to but excluding n−1. For [4, 2], what is actual versus expected?
4. Rule: low if x < 4, mid if x < 9, otherwise high. The second comparison was wrongly ≤ 9. Which regression test should be kept?

The download contains your current choices and any checked feedback. Keep the separate transfer-task work in your own document; downloading its instructions does not mark it complete.

Use the skills in a new task

Specify and repair sum_small(values): accepts lists of 0–3 integers, each in 0..9, and returns their sum; other inputs return invalid. Draft loop excludes the last position. Write and trace tests [], [6], [2,3], [10] and [1,2,3,4], repair the loop and retain a regression test.

Work on paper or in your own document. Explain the choices you made.

  • Reject [10] for an out-of-range element and [1,2,3,4] for excess length.
  • Expected accepted sums: 0, 6 and 5.
  • Explain faulty outputs 0, 0 and 2 for the accepted tests.
  • Repair to visit all positions 0..n−1 and retain [6] → 6.
Compare with a model response

First validate list length ≤ 3 and every element an integer in 0..9, with Boolean values excluded. Invalid cases: [10], [1,2,3,4]. For accepted [], [6], [2,3], expected sums are 0,6,5; the faulty loop returns 0,0,2. Set total = 0 and loop i from 0 up to but excluding n, adding values[i]. Retesting returns 0,6,5. Keep [6] → 6 as a regression test for the skipped-last-element error.

A different response can also meet the criteria. Compare the evidence and reasoning, rather than copying the wording.