Capture equivalence across the input space
See this course’s project requirements
A before/after fictional fee calculator split into pure functions with an executable equivalence suite, clearer names and documented intentional nonchanges.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- Produce a complete valid/rejected behavior contract and intentional-change boundary.
- Retain full finite valid-space coverage and explicitly scoped invalid-case comparisons.
- Create checked validation/subtotal helpers and preserve the public entry contract.
- Produce a domain-name/reference review with unchanged discount and delivery semantics.
- Retain a passing baseline and an expected failing price mutation without altering final pricing.
- Deliver an independently reasoned, repeatable refactor with finite coverage and selected-invalid limits.
Review and revise
Use these criteria to check your work and choose what to improve.
- The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
- Normal, boundary and rejected cases are recorded with expected versus observed results.
- The changed case has a correct explanation and does not rely on hidden state.
- The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Want more background?
The idea in everyday life
Fictional workshop kits: quantity 1–20, $3 per kit, a 20% member discount on kit subtotal, and $2.50 only for post. Calculations return integer cents. legacy_fee.py and refactored_fee.py must agree on permitted and rejected requests.
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
Capture equivalence across the input space — original worked practice
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
Fictional workshop kits: quantity 1–20, $3 per kit, a 20% member discount on kit subtotal, and $2.50 only for post. Calculations return integer cents. legacy_fee.py and refactored_fee.py must agree on permitted and rejected requests.
1. Step 1
Read test-equivalence.py iterating 20 quantities, two member flags, and two delivery modes.
You should see: There are 80 valid combinations.
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
2. Step 2
Inspect result(fn,args), which records either a value or ValueError type/message.
You should see: Successful and rejected behavior are compared in a consistent form.
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
3. Step 3
Run python3 test-equivalence.py before making further edits.
You should see: 88 refactor equivalence cases passed.
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
4. Step 4
Retain the 80 valid plus 8 invalid coverage description and actual output.
You should see: A baseline equivalence-suite record.
Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination.
What to finish
Retain full finite valid-space coverage and explicitly scoped invalid-case comparisons.
Watch for this
Claiming selected invalid examples exhaust every possible malformed Python object.
How can I tell I understand it?
Demonstrate the rule: Characterization tests record current behavior across meaningful cases. Here the valid input space is small enough to enumerate every declared combination. Use the supplied variant to distinguish a changed result from a broken implementation.
Quick knowledge check
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Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
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