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Course Library · Lesson 2 of 6
Digital · Guided lesson

Choose cases that expose mistakes

About 28 minutes · 6 reading + 22 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
See this course’s project requirements

Review the Room Picker simulation from initial contract through a verified rule repair.

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Define scope and observable acceptance criteria.
  • Record eight diverse cases with expected and observed outcomes.
  • Write a minimal reproducible bug report with impact.
  • Show a one-change repair experiment and relevant comparisons.
  • Deliver retest evidence and a usability hypothesis with honest limits.

Review and revise

Use these criteria to check your work and choose what to improve.

  • Coverage: cases represent relevant classes and boundaries.
  • Reproducibility: state, steps and results are sufficient to repeat.
  • Reasoning: the repair follows evidence and preserves valid behavior.
  • Handoff: claims stay within the observed version and scope.
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Before you begin

The idea in everyday life

Testing every possible value is usually impractical. A small deliberate set can reveal more than repeated comfortable examples. Room Picker has a short range rule, so its edges are especially informative. You will build cases from the contract before consulting a supplied behavior table, which prevents observed defects from quietly rewriting your expectations.

The idea

Cover different kinds of input, then check where one kind turns into another.

Try it

One step at a time.

Use the sample or information you have permission to use. Keep your work as you go. You can pause between steps.

  1. 1

    Choose one ordinary valid request, such as three seats at Cedar. Add the valid endpoints one and six, plus the neighboring invalid values zero and seven.

  2. 2

    Add a fractional request of 2.5, a blank seat field and a missing session. These cases test different conditions, so they are more informative than seven ordinary valid numbers.

  3. 3

    For each case, record the input, starting conditions (preconditions), action, and expected screen or message. Keep the session the same except when testing a missing session.

  4. 4

    Compare with the supplied v1 observations: 1 and 3 reach Review; 6 is rejected; 0 and 7 are rejected; 2.5 is rejected; blank is rejected; no session is rejected.

  5. 5

    Mark the six-seat case failed and preserve all other observations. Record only the actual scope: this table checks the listed inputs, not every possible string, locale or future product version.

Example

See how it works.

Fictional test plan contains eight cases: Cedar with seats 0, 1, 3, 6, 7, 2.5 and blank, plus seats=3 with no session. The contract expects Review only for 1, 3 and 6. Version 1 produces Review for 1 and 3 but rejects 6, while all five invalid cases are rejected as expected. Therefore seven cases pass and one fails. This does not mean the product is "87.5% correct" in real use; the cases were deliberately chosen rather than sampled from user behavior. The failed endpoint gives a focused next investigation.

Check your work

Did you cover these?

  • Both endpoints and their neighbors are included.
  • Expected behavior is separate from observed behavior.
  • Only seats=6 fails the supplied range cases.
Your work

What to finish

An eight-case plan with expected results, supplied observations and statuses.

Common mistake

Watch for this

Testing only convenient middle values and missing the range endpoints.

How can I tell I understand it?

Explain why each case adds coverage and identify the failed boundary.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1A valid range is 10–20 inclusive. Which pair tests the upper boundary most directly?
2Ten cases pass and one fails. What can you conclude?
3You already tested 3, 4 and 5 in a 1–6 range. Which new case most broadens coverage?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
2
Finish this lesson

Pass the check. We’ll save the progress.

Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

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Sources and further reading

Explore the references behind this lesson.

MIT 6.031 — Reading 3: Testing
Source & access notes · checked 2026-09-10

Read systematic testing and boundary discussion. Original reservation examples and questions do not reproduce the university exercises.

Access: Free public university reading; examples on the source page assume more programming experience. No enrollment, credit or certificate is needed for the adapted beginner concepts here.

Reuse: Linked for reference. Examples, activities and assessments here are original; free access alone does not grant permission to reuse source text or branding.

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