Choosing test data for an algorithm

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Quick Questions

Shade in the A or B circle for each question.

1. Which describes good test data for an algorithm?

A Chosen inputs, each with the output you expect

B Any random numbers with no expected output

2. An algorithm has 3 branches (if, else if, else). How many tests do you need at least?

A 1 test is enough

B 3 tests, one for each branch

3. When should you work out the expected output?

A After you see what the algorithm gives you

B Before you run the algorithm

4. if mark >= 50 then print "Pass" else print "Fail". Which test data covers both branches?

A mark = 70 (expect Pass) and mark = 30 (expect Fail)

B mark = 70 and mark = 80 (both expect Pass)

5. After you run a test, what do you compare?

A The real result with the expected output

B The real result with the input value

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1Test: mark = 75, expected = "Pass"		AThe test cases have no expected output, so you cannot tell whether the real result is right or wrong.
2Tests: age = 8, age = 14, age = 30		BInput: 40 -> Expected: "Fail"
3Write down the expected output before you run the test, so you can compare it with the real result		CAll three test values go down the same branch (Pass). Nothing tests the else branch, so a mistake there would never be found.
4An if-then-else has two branches, so you need at least two tests, one for each branch		DTest data with one test for each branch: a child, a teen and an adult path
5if mark >= 50 then print "Pass" else print "Fail" Tests: 60, 70, 90		EOne test case: a chosen input paired with the output you expect before running the algorithm
6Tests: input = 5, input = 12 (no expected output written)		Fif score >= 50 then: Tests: 80 and 20

Definitions

test data

Fill in the Blanks

Complete each line of code by filling in the missing parts.

if mark >= 50 then print "Pass" else print "Fail" Test: mark = 30, ________ = "Fail"

Algorithm has 3 branches (if, else if, else) One test per branch means _ tests

if mark >= 50 then print "Pass" Test: ____ = 50, expected output "Pass"

actual ← 20 expected ← 20 if actual _ expected then print "Match"

if age >= 18 then fee ← 10 else fee ← 5 Test: age = 12, expected fee = _

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A # Rule: mark >= 50 is a Fail

B # Test 1: 70, expect Pass

C # Test 2: 30, expect Fail

Question 2

A # Ticket: under 13 = Child

B # 13-17 = Teen, 18+ = Adult

C # Test 1: 8, expect Child

D # Test 2: 15, expect Adult

E # Test 3: 30, expect Adult

Question 3

A if n > 0 then print Positive

B else print Not positive

C Test 1: 5, expect Positive

D Test 2: 0, expect Positive

Question 4

A if x > 10 then print Big

B else print Small

C Test 1: 30, expect Small

D Test 2: 20, expect Big

Question 5

A # Free delivery if cost >= 50

B # Test 1: 60, expect Pay $5

C # Test 2: 20, expect Pay $5

Answer Key

Choosing test data for an algorithm

Section A: Quick Questions

A — Chosen inputs, each with the output you expect

B — 3 tests, one for each branch

B — Before you run the algorithm

A — mark = 70 (expect Pass) and mark = 30 (expect Fail)

A — The real result with the expected output

Section B: Match the Pairs

Test: mark = 75, expected = "Pass" → One test case: a chosen input paired with the output you expect before running the algorithm

Tests: age = 8, age = 14, age = 30 → Test data with one test for each branch: a child, a teen and an adult path

Write down the expected output before you run the test, so you can compare it with the real result → Input: 40 -> Expected: "Fail"

An if-then-else has two branches, so you need at least two tests, one for each branch → if score >= 50 then: Tests: 80 and 20

if mark >= 50 then print "Pass" else print "Fail" Tests: 60, 70, 90 → All three test values go down the same branch (Pass). Nothing tests the else branch, so a mistake there would never be found.

Tests: input = 5, input = 12 (no expected output written) → The test cases have no expected output, so you cannot tell whether the real result is right or wrong.

Section C: Definitions

test data — Chosen inputs, each with the output you expect, picked so every path (branch) through an algorithm gets tested. Compare the real result to the expected output.

Section D: Fill in the Blanks

if mark >= 50 then print "Pass"
else print "Fail"
Test: mark = 30, expected = "Fail"

Algorithm has 3 branches (if, else if, else)
One test per branch means 3 tests

if mark >= 50 then print "Pass"
Test: mark = 50, expected output "Pass"

actual ← 20
expected ← 20
if actual = expected then print "Match"

if age >= 18 then fee ← 10 else fee ← 5
Test: age = 12, expected fee = 5

Section E: Spot the Error

A — The rule does not match the tests. A mark of 50 or more should be a Pass, so the rule should say 'is a Pass'. Test data only works if the expected outputs follow the rule.

D — An input of 15 is in the 13-17 range, so the expected output is Teen, not Adult. Each test needs the correct expected output for its branch.

D — 0 is not greater than 0, so the else branch runs. The expected output should be 'Not positive'.

C — 30 is bigger than 10, so it would print Big. To test the else branch, use an input of 10 or less, such as 3. Then there is one test per branch.

B — 60 is at least 50, so the order gets free delivery. The expected output should be 'Free'.