Testing CS Thinking Example 2

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Example 2

medium
A program grades students: 90-100 = A, 80-89 = B, 70-79 = C, 60-69 = D, below 60 = F. Design a complete set of test data including boundary values.

Solution

  1. 1
    Step 1: Normal values: 95 (A), 85 (B), 75 (C), 65 (D), 50 (F). One from each grade band.
  2. 2
    Step 2: Boundary values: 100, 90, 89, 80, 79, 70, 69, 60, 59, 0. These are at the edges where the grade changes.
  3. 3
    Step 3: Erroneous values: -5, 101, 'abc'. These should be rejected or handled. Boundary testing is crucial because off-by-one errors are extremely common.

Answer

Normal: one per grade. Boundary: values at each grade boundary (90, 89, 80, 79...). Erroneous: negative, >100, non-numeric.
Systematic test design covers normal, boundary, and erroneous cases. Boundary values are where most bugs occur, especially off-by-one errors in conditional statements.

About Testing

Systematically running a program with known inputs to verify that its outputs are correct. Testing involves designing test cases that cover normal inputs, boundary values, and error conditions, then comparing actual results against expected results.

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