← QCE Digital Solutions Unit 4

Testing a prototype for accuracy

Comparing the prototype's actual output with expected results worked out by hand from known data, to find wrong values such as rounding or conversion errors.

Part of: QCE Digital Solutions Unit 4 — Prototype Digital Data Exchanges — Module 128

Understanding Testing a prototype for accuracy in QCE Digital Solutions Unit 4

What it does: The hand-calculated expected result is stored first, then compared with the actual output from the prototype. int() cuts off the decimal part, giving 2, but round(2.5, 1) keeps 2.5. Comparing against the hand-calculated 2.5 reveals the error. By hand: 3 x 2.50 = 7.50. GST is 0.75. Total is 8.25. Accuracy testing looks for changes between what was received and what is displayed, such as a truncated or wrongly converted number. Layout is a usability matter. Accuracy is about whether values are correct, not whether the code runs. Wrong rounding or conversions give no error message.

Common mistakes: The conversion formula is upside down. By hand, 25 * 9 / 5 + 32 = 77.0, but 5 / 9 gives about 45. The test would fail because of a formula error, so the line should be celsius * 9 / 5 + 32. int() truncates 19.999 to 19 instead of rounding it. The hand-calculated expected value is 20.0, so the prototype must round with round(price, 1).

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Learning

Duo

Which is the correct way to get the expected result in an accuracy test?

Work it out by hand from known input data before running the prototypeCopy whatever the prototype outputs and call it expected

Matches

expected = average([70, 80, 90]) assert average([70, 80, 90]) == expected

↓

The expected value is produced by the program itself, not worked out by hand, so the test always passes and proves nothing.

Applying

Meanings

Term

accuracy testing

Meaning

Comparing the prototype's actual output with expected results worked out by hand from known data, to find wrong values such as rounding or conversion errors.

Practice

def to_fahrenheit(c):

Testing

Gaps

print(actual expected)

Check Answer

Spots

2expected = 77.0

3actual = celsius * 5 / 9 + 32

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Quick Questions

1. Which is the correct way to get the expected result in an accuracy test?

A. Work it out by hand from known input data before running the prototype ✓

B. Copy whatever the prototype outputs and call it expected

Expected results must come from an independent source, such as a hand calculation. If you copy the prototype's output, the test can never fail.

2. A weather API sends 22.0 degrees Celsius. Your prototype should display Fahrenheit. Which expected value is worked out by hand correctly?

A. 54.0 (22 x 9 / 5 - 32 + 32 - 22 + 54)

B. 71.6 (22 x 9 / 5 + 32) ✓

By hand: 22 x 9 / 5 = 39.6, then + 32 = 71.6. The expected value is calculated from the known input before checking the output.

3. The prototype receives a price of 4.995 and displays 5.00 when the spec says to round to 2 decimal places. What does the test show?

A. It matches only if the hand-calculated expected value is 5.00 under the stated rounding rule ✓

B. It always fails because the numbers are different

Rounding errors depend on the rule used. Decide the rounding rule first, calculate the expected value by hand, then compare.

4. Test data: 3 items at $2.50 each with 10% GST added. Which expected total should you record?

A. $7.75

B. $8.25 ✓

By hand: 3 x 2.50 = 7.50. GST is 0.75. Total is 8.25.

5. Which check compares received vs displayed data?

A. Compare the value in the API response with the value shown on screen ✓

B. Check that the screen layout looks neat

Accuracy testing looks for changes between what was received and what is displayed, such as a truncated or wrongly converted number. Layout is a usability matter.

Match the Pairs

assert round(c * 9 / 5 + 32, 1) == 98.6 → Checks the converted temperature matches the answer worked out by hand for a known input of 37 degrees Celsius

print(received == displayed) → Compares the data received from the API with the data shown on screen to see if it changed on the way

Work out the expected value by hand first (3 items at 4.50 = 13.50), then compare it with the program's total → expected = 13.50 actual = total_cost(3, 4.50) print(actual == expected)

A rounding error appears when the output differs from the expected value, for example 2.5 shown as 2 → print(int(2.5), round(2.5, 1))

expected = average([70, 80, 90]) assert average([70, 80, 90]) == expected → The expected value is produced by the program itself, not worked out by hand, so the test always passes and proves nothing.

assert price_with_gst(100) == 10.0 → The expected result was worked out wrongly. 100 plus 10% GST should be 110.0, so the test checks against the wrong value.

Key Term

accuracy testing

Comparing the prototype's actual output with expected results worked out by hand from known data, to find wrong values such as rounding or conversion errors.

Fill in the Blanks

1. expected = 59.97 actual = round(19.99 * 3, 2) print(actual == expected)

Hint: Type the comparison operator that checks whether the actual output equals the hand-calculated expected value.

2. total = 10 / 3 shown = round(total, 2) print(shown)

Hint: Type the built-in function that rounds a number to a set number of decimal places, so the output can be checked against 3.33 worked out by hand.

3. expected = 212 actual = 100 * 9 / 5 + 32 print(actual == expected)

Hint: Type the arithmetic operator that multiplies the Celsius value in the conversion formula. The hand-calculated result for 100 C is 212 F.

4. received = 42.5 displayed = float("42.5") print("Mismatch:", received != displayed)

Hint: Type the comparison operator that is True when the received value and the displayed value are different.

5. expected = 59.97 actual = 19.99 * 3 print(abs(actual - expected) < 0.01)

Hint: Type the built-in function that gives the size of the difference between actual and expected, ignoring whether it is positive or negative.

Spot the Error

Question 1

A celsius = 25

B expected = 77.0

C actual = celsius * 5 / 9 + 32

D print(actual == expected)

Line C — The conversion formula is upside down. By hand, 25 * 9 / 5 + 32 = 77.0, but 5 / 9 gives about 45. The test would fail because of a formula error, so the line should be celsius * 9 / 5 + 32.

Question 2

A price = 19.999

B expected = 20.0

C shown = int(price)

D print(shown == expected)

Line C — int() truncates 19.999 to 19 instead of rounding it. The hand-calculated expected value is 20.0, so the prototype must round with round(price, 1).

Question 3

A marks = [80, 70, 90]

B expected = 240

C avg = sum(marks) / len(marks)

D print(avg == expected)

Line B — The hand calculation is wrong. The total is 240, but the average needs 240 / 3 = 80. An incorrect expected value makes the accuracy test meaningless.

Question 4

A received = {'temp': 21.5}

B shown = received['temp']

C assert shown == 215

Line C — The received data says 21.5, so the displayed value must be compared with 21.5. Writing 215 drops the decimal point and would wrongly report a display error.

Question 5

A km = 12.5

B miles = km * 0.621371

C want = 7.77

D print(round(miles, 1) == want)

Line D — By hand, 12.5 * 0.621371 = 7.7671, which is 7.77 to 2 decimal places. Rounding to 1 place gives 7.8, so the comparison fails. It should be round(miles, 2).

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