← VCE Software Development U3O1

Boundary test values

Test inputs at the edge of a condition. For age >= 18, test 17 (just below), 18 (exactly on) and 19 (just above) to check the algorithm picks the right path at the edge.

Part of: VCE Software Development - U3O1 - Programming — Module 173, VCE Software Development - U4O1 - development and evaluation — Module 158, VCE Data Analytics - U3O1 - Data Analytics — Module 142, 7-8 Digital Technologies: Designing and tracing algorithms — Module 37, VCE Applied Computing U1O2 Programming: Testing and debugging — Module 7, ACARA Digital Technologies Years 7–8 — Tracing and Debugging Algorithms — Module 43, ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (Python) — Module 70, ACARA Digital Technologies Years 9–10 — Testing and Validating Programs — Module 6, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 44

Understanding Boundary test values in VCE Software Development U3O1

What it does: The edge of score > 50 is 50, so the tests are 49 (just below), 50 (exactly on) and 51 (just above). The boundary number is the one written in the condition. 51 is just above it. Mistakes with >= and > only show up when we test the exact boundary value. 100 is far from the edge. You also need values like 49, 50 and 51 to check the boundary. With >, the value 18 would wrongly go down the 'no' path. 25 passes both versions, so the bug stays hidden. The value 18 sits exactly on the edge of age >= 18, so it shows whether >= was written correctly.

Common mistakes: 18 is exactly on the boundary. Because the condition uses >=, 18 is included and prints 'Adult'. The line should be: Test 18 -> Adult. Boundary tests need values just below, exactly on and just above the edge. 10 and 90 are far from 50. The line should be: Test values: 49, 50, 51.

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Learning

Duo

An algorithm checks: if age >= 18 then print "Adult". Which set of test values are boundary values?

5, 40, 9017, 18, 19

Matches

Condition: age >= 18. Tests: 5, 10, 90

↓

These values are all far from the boundary. They should include 17, 18 and 19 to test the edge.

Applying

Meanings

Term

Boundary values

Meaning

Test inputs at the edge of a condition. For age >= 18, test 17 (just below), 18 (exactly on) and 19 (just above) to check the algorithm picks the right path at the edge.

Practice

// Condition: age >= 18

Testing

Gaps

age <- (just below the edge)

Check Answer

Spots

2 print 'Adult'

3Test 18 -> no output

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Quick Questions

1. An algorithm checks: if age >= 18 then print "Adult". Which set of test values are boundary values?

A. 5, 40, 90

B. 17, 18, 19 ✓

Boundary values sit at the edge of the condition: just below (17), exactly on (18) and just above (19).

2. For the condition score > 50, which value is exactly on the boundary?

A. 50 ✓

B. 51

The boundary number is the one written in the condition. 51 is just above it.

3. For the condition temperature < 30, which value is just below the boundary?

A. 29 ✓

B. 31

Just below 30 is 29. 31 is just above the boundary.

4. Why do we test 18 when the condition is age >= 18?

A. To check the algorithm takes the right path at the exact edge ✓

B. Because 18 is a lucky number for testing

Mistakes with >= and > only show up when we test the exact boundary value.

5. A game gives a bonus if lives > 0. Which test values check the boundary?

A. 10, 20, 30

B. -1, 0, 1 ✓

The boundary is 0, so test just below (-1), exactly on (0) and just above (1). Whole-number lives could also use 0 and 1 as the key pair.

Match the Pairs

age >= 18 with test value 18 → A value exactly on the boundary, which checks that the condition includes the edge value

age >= 18 with test value 17 → A value just below the boundary, which should make the condition false

Boundary test values for score > 50: just below, exactly on and just above the edge → Test with 49, 50 and 51

A value just above the boundary checks the true path starts right after the edge → temp > 30 tested with 31

Condition: age >= 18. Tests: 5, 10, 90 → These values are all far from the boundary. They should include 17, 18 and 19 to test the edge.

Condition: mark > 50. Tests: 49, 51, 52 → The exact boundary value 50 is missing. Add 50 to check that > does not include the edge.

Key Term

Boundary values

Test inputs at the edge of a condition. For age >= 18, test 17 (just below), 18 (exactly on) and 19 (just above) to check the algorithm picks the right path at the edge.

Fill in the Blanks

1. if age >= 18 then age <- 17 (just below the edge)

Hint: Type the test value that is just below the boundary in the condition.

2. Tests for price < 20: 19, 20, 21

Hint: Type the test value that sits exactly on the boundary.

3. Tests for mark >= 50: 49, 50, 51

Hint: Type the test value that is just above the boundary.

4. Tests for speed > 60: 59, 60, 61

Hint: Type the test value that is just below the boundary number.

5. if age >= 18 then Tests: 17 no, 18 yes, 19 yes

Hint: Type the comparison operator that makes the exact boundary value pass.

Spot the Error

Question 1

A if age >= 18 then

B print 'Adult'

C Test 18 -> no output

D Test 17 -> no output

Line C — 18 is exactly on the boundary. Because the condition uses >=, 18 is included and prints 'Adult'. The line should be: Test 18 -> Adult.

Question 2

A if score > 50 then

B Test values: 10, 50, 90

C Expected: fail, fail, pass

Line B — Boundary tests need values just below, exactly on and just above the edge. 10 and 90 are far from 50. The line should be: Test values: 49, 50, 51.

Question 3

A if temp > 10 then

B print 'Wear a jumper'

C Test 9 -> Wear a jumper

D Test 10 -> no jumper

Line A — The test results show 9 prints 'Wear a jumper' and 10 does not, so the condition must be temp < 10. Using > flips the edge and breaks the tests.

Question 4

A Condition: age >= 13

B Just below: 12

C Exactly on: 15

D Just above: 14

Line C — The value exactly on the boundary is the number in the condition, which is 13. 15 is not on the edge. The line should be: Exactly on: 13.

Question 5

A input mark

B if mark > 50 then

C print 'Pass'

D else

E print 'Fail'

F Test 50 -> Pass

Line B — The test says 50 should pass, but with > the value 50 is not included and would print 'Fail'. The condition should be mark >= 50.

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