Test the whole input contract
Which tests expose a missing input guard?
Entering midway? Revisit Make a passing test suite reveal a bug for the preceding worked example, or start here and use the explanation below.
Start with a concrete question
A synthetic quote function charges 3×quantity+2 for positive quantities and zero otherwise. Its buggy version applies the formula to every quantity.
Try the initial inputs, then write a prediction before changing one setting. All calculations run locally on your CPU.
What do you expect?
Predict whether tests at quantities 2 and 4 can prove behavior at zero.
Change one thing. Inspect what happens.
- Run positive-only tests and explain their coverage gap.
- Add zero and negative cases separately.
- Implement the repaired function and print pass/fail for at least five cases, including an unseen positive input.
Your settingsMechanism
Calculation belowEvidence
Compare outcomes
Compare the current results
Every bar starts at zero and uses the same numeric scale in this chart. The upper bound automatically adjusts to the largest current value (at least 1), so compare the numbers when changing inputs. Units and quantities come from each label; different kinds of quantity are not interchangeable. Displayed values are rounded to at most six significant digits.Follow the calculation
- Quantity 2: contract 8, actual 8 → PASS.
- Quantity 4: contract 14, actual 14 → PASS.
The tool contract charges zero for nonpositive quantities. Positive-only examples cannot expose the missing guard.
Implement a function and independent test oracle
Repair quote using the contract. Keep the expected array independent of the function. Five true outputs mean these five tests passed; add a fresh case and its independently calculated expected value.
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Compare with my earlier draft
function quote(q) { return 3 * q + 2; }
const inputs = [-2, 0, 1, 4, 7];
const expected = [0, 0, 5, 14, 23];
for (let i = 0; i < inputs.length; i++) {
print(quote(inputs[i]) === expected[i]);
}Explain what you changed and why in your observation notes. Text differences do not establish quality.
Inspect an example solution after your attempt
function quote(q) {
if (q <= 0) { return 0; }
return 3 * q + 2;
}
const inputs = [-2, 0, 1, 4, 7];
const expected = [0, 0, 5, 14, 23];
for (let i = 0; i < inputs.length; i++) {
print(quote(inputs[i]) === expected[i]);
}This is one worked example. Test another input and explain its limitations.
Captures keep your inputs, prediction and observation. Results are recalculated from those inputs. Resetting inputs keeps your captures and challenge history.
Explain the mechanism
Test the whole input contract
A synthetic quote function charges 3×quantity+2 for positive quantities and zero otherwise. Its buggy version applies the formula to every quantity.
Predict before changing inputs
Predict whether tests at quantities 2 and 4 can prove behavior at zero.
Understand the mechanism
Partition an input space by behavior. Positive, zero and negative inputs trigger different obligations in this contract.
The formula returns 2 at quantity zero, but the contract requires 0. At −2 it returns −4, also invalid.
A test oracle is the expected answer derived independently from the contract. Copying the implementation formula into every expected answer would repeat the same bug.
Calculate it yourself
quote(q)=0 when q≤0; otherwise quote(q)=3q+2.
Guided investigation
Run positive-only tests and explain their coverage gap.
Add zero and negative cases separately.
Implement the repaired function and print pass/fail for at least five cases, including an unseen positive input.
Assumptions and limitations
The model accepts bounded integer examples only. A real interface must also address nonnumbers and missing data.
Passing the fixture does not establish total correctness; the independent implementation task requires broader evidence.
Further investigations
High school: Write a table of inputs, expected outputs and reasons before coding.
College: Add invariant tests and compare against a separately authored oracle.
Working professionals: Produce a regression test and failure report for an input-validation defect.
Your implementation or data task
Repair quote using the contract. Keep the expected array independent of the function. Five true outputs mean these five tests passed; add a fresh case and its independently calculated expected value.
Use the editable workspace on this page. Its output is practice evidence; explain why it satisfies the contract and test a fresh case.
Try a fresh case
Under the same contract, what is the quote for a previously untested quantity of 7?
This is a public practice check. Retries support learning; matching a number does not certify independent proficiency.
Take the investigation further
Choose any extension. These are project prompts for you to carry out; they are not automatically assessed.
School investigation
Write a table of inputs, expected outputs and reasons before coding.
College investigation
Add invariant tests and compare against a separately authored oracle.
Workplace investigation
Produce a regression test and failure report for an input-validation defect.
Keep the evidence, choose your next step
Completion records your own decision that you have worked through this investigation. Practice checks and independent project evidence are separate.